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CHAPTER 12

INSTRUMENTS FOR MULTIPLE SPECIFIC GASES AND VAPORS:

GC, GC/MS, AND IR

This chapter describes direct-reading instruments

that can identify and measure the concentrationof specific compounds in an airborne mixture.Basically this includes two types of instruments:

• Gas chromatograph (GC or GC!massspectrometer (GC!"# de$ices that separatethe airborne compounds so that each can beidentified and its concentration measured asthe separated compounds pass through thedetector.

• %nfrared (%& instruments where thewa$elength of the emitted %& radiation can bead'usted to match the wa$elength that

specific chemical compounds absorb the %&radiation. #ince many chemicals ha$e acharacteristic absorption wa$elength thismethod can pro$ide an accurate method ofidentification. )dditionally since the amountof %& radiation absorbed is proportional to theconcentration of the chemical theseinstruments pro$ide concentration data.

)s noted in pre$ious chapters there is some

o$erlap between these instruments and thede$ices co$ered in earlier chapters. #pecificallymany %& de$ices are a$ailable that are set to emit 'ust one wa$elength of %& radiation and thus arespecific to one airborne compound. )s anillustration direct-reading instruments for carbondioxide (C*+ often are based on the %& principleand they use the absorption of %& radiation at awa$elength of ,.+ 'am to measure theconcentration of C*+ in the air. owe$er theseinstruments are co$ered in detail in this chapter(instead of Chapter /* 0%nstruments with #ensorsfor #pecific Chemicals0 as part of the o$erall

discussion of %& instruments.The GC GC!"# and %& instruments that can

determine the concentrations of multiple specificcompounds in an airborne mixture are high-endde$ices that are expensi$e and sophisticated andcan be complicated to operate. Generally theyare only used when less expensi$e and easier touse de$ices are not ade1uate for the monitoring 'ob.

Air Monitoring for Toxic Exposures, Second Edition. Byenry 2. "c3ermott %#B4 *-,/-,5,65-, 7 +**, 2ohn

8iley 9 #ons %nc.

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.12 INSTRUMENTS FOR MULTIPLE SPECIFIC GASES ANDVAPORS: GC, GC/MS, AND IR

8hile these instruments ha$e importantdifferences they ha$e se$eral characteristics incommon:

• )ll are designed to be used with a personalor laptop computer either to operate theinstrument or to manage the data. Thecompound identification and measurementsteps in$ol$e comparing the airbornesample to stored calibration or library dataand so a computer is essential for this step.They also generate large amounts of data

for each measurement and these must be processed in a computer.

• 8hile many configurations and options area$ailable the sampling practitionergenerally describes their needs(compounds to be sampled possibleinterferences operating conditions etc. tothe manufacturer who first determines iftheir technology is a suitable fit for theapplication. %f so the manufacturerstechnical staff then selects and configuresthe instrument to meet the users specificneeds. ;or this reason there is less needfor the sampling practitioner to understandthe $arious instrument options with thegoal of selecting these options on theirown as is typical for less sophisticateddirect-reading instruments.

• <$en though these instruments are themost sophisticated direct-readinginstruments a$ailable they still are notdesigned to identify the components of acompletely un=nown or 0mystery0 airbornemixture. The instruments achie$e theiraccuracy in identifying and measuring the

concentration of indi$idual chemicalcompounds by being calibrated with thespecific compounds they are measuring.;or all of these de$ices daily or morefre1uent calibration using a =nowncalibration gas mixture containing each ofthe components of interest is recommendedfor optimal performance.

• Because of their si>e and complexitythey are not routinely used for directoccupational exposure measurementsof breathing >one concentration. "oretypically they are used for area or source sampling? for en$ironmentalreasons? at ha>ardous waste sites? for field determination of the compositionof an airborne mixture for real-timerespirator selection decisions? or as anaid to understanding the total @ACreading of a less sophisticated instru

ment such as a photoioni>ation detector (%3. There are some 4%A#occupational sampling methods for field GCs? one is described later in thischapter. ;or integrated samples a

personal pump can be used to fill asampling bag for analysis using theGC or %& instrument.

The instruments described in thischapter meet these criteria:

• They are 0portable0 in that they are battery-powered and can be carried aroundin the field or set up in a temporarylocation.

• They can measure airborne contaminantsalthough most can measure 0headspace0le$els ($apor collected abo$e li1uid orsolid samples and some can analy>eli1uid samples directly.

• They are commercially a$ailable field-ready technology.

PORTABLE GASCHROMATOGRAPHS (GCs)

)s discussed in Chapter / gas chromatog-raphy (GC is a common laboratory analyticalmethod for gases and organic $apors that arecollected using charcoal tubes or anothersample collection de$ice. The GC operates onthe principle that a $olatili>ed sample is mixedwith a carrier gas and



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PORTA3LE GASC4ROMATOGRAP4S *GCs-

.15

Figure 12.1. 3iagram of a typical gas chromatograph. (Courtesy of

%nternational #ensor Technology.

in'ected into a column that separates thecomponents in the sample according to thetime it ta=es the component to tra$el throughthe column (;igure /+./. )s the moleculesemerge from the column a detector measuresthe amount of each material. An achromatogram each emerging compound isrepresented by a 0pea=0 based on its elutiontime. Component identification is made usinga data 0library0 de$eloped by in'ectingsamples of =nown chemicals into the columnand measuring the tra$el time for each. Theconcentration of each material is representedby the area under its pea= on thechromatogram (;igure /+.+. ;or laboratoryGC units a wide choice of columns detectorsand operating parameters such as temperature

programming gi$e the GC the ability toidentify many different chemicals especiallythose in mixtures.

ortable GCs as described in this chapterfocus on modern high-end portable gaschromatographs. #ome earlier field GCs wererelati$ely simple instruments that essentiallyadded a short separation column maintained atambient temperature to a %3 instrument.These simple units ha$e been supplantedbecause they do not pro$ide much ad$antagebeyond the direct-reading instruments with

sensors for specific chemicals discussed in

Chapter /*. The GCs co$ered in this chaptermore closely resemble laboratory instrumentswith heated columns temperature

programming and a choice of columns anddetectors based on the compounds of interestand possible interferences. These instrumentsre1uire a computer to control the de$icesoperation and pro$ide the data managementsystem. #ome re1uire a laptop computer to beused along with the instrument in the fieldwhile for others an office computer issufficient to transfer information between thede$ice and computer. The instrumentmanufacturer supplies a proprietary software

pac=age that operates the GC collects storesand processes data and then downloads it tothe hard dis= dri$e. These GCs measure

concentrations ranging from parts-per-trillion(ppt to percent ( le$els. #ome allowcontinuous unattended operation or can becontrolled from a remote location using amodem and communications lines. Thesesophisticated computer-controlled instruments

pro$ide the functions that are described below.

Instrument Calibration. The instrumentshould be calibrated with each chemical thatwill be measured in the field. 3uring thismode the system introduces a sample of a

=nown calibration mixture into the



.16




.1.

system and performs chromatographicanalysis either when the user initiates thecalibration cycle or at preset fre1uencies. Theinstrument then displays this calibrationchromatogram including the nameconcentration le$el and retention time of eachcompound in the calibration mixture. The areaunder each pea= is integrated and theconcentration le$el of the standard is assignedto this pea= area. There are two calibration

methods commonly used/:

• "ultipoint calibration is most accurate. %tin$ol$es introducing se$eral differentconcentration le$els of a chemical to theGC and plotting a cur$e of pea= areas(hori>ontal axis $ersus concentrationle$el ($ertical axis. 8hen an un=nownconcentration of the same chemical isdetected in the system the area obtained iscompared to the calibration cur$e todetermine its concentration le$el. This

method is $ery accurate and can co$er alarge concentration range.

• #ingle-point calibration method is oftenused for portable gas chro-matography. %tsaccuracy within a reasonableconcentration le$el range is satisfactoryand it is easy to perform. ) calibrationcur$e similar to the multipoint cur$e isdrawn using only two points. Ane is >erowith an assumed area pea= count of >ero.The other point is the point area obtainedwhen a =nown concentration of the

standard is in'ected at its concentrationle$el. This cur$e is used to calculateanalysis results. This method is relati$elysimple and re1uires only one concen-tration for calibration.

#ingle calibration is a$ailable for allinstruments? multipoint calibration is anoption for others. #ome de$ices ha$e aninternal cylinder containing the calibrationmixture while others use an external cylinderor calibration bag sample.

Calibration gas mixtures can be purchasedfrom commercial suppliers or prepared by thesampling practitioner as described in)ppendix B. ) 0ready-to-use0 calibrationmixture is most con$enient to use or a higherconcentration mixture that is diluted by thesampling practitioner with pure air into acalibration bag will gi$e more calibration runsfrom the calibration cylinder. Theconcentration of each gas in the final

calibration mixture should be near theconcentration of interest. Chec= with thecalibration gas supplier to determine if thecompounds will be stable in the cylinder when

blended at the desired concentrations.

Sample Collection and Injection. Theinstruments may offer up to three differentways for sample introduction:

• 3irect on-column in'ection using asyringe. There are different syringe types

for air samples and for li1uid samples.@olumes of air samples in'ected to thecolumn are typically +mD or less while$olumes of li1uid samples in'ected to thecolumn can range up to +uD. )1ueous andsoil samples can be extracted with anorganic sol$ent prior to direct in'ection.

• Esing a concentrator, which is a smalltube pac=ed with an adsorbent materialsuch as Tenax attached to the internalsampling pump. The airborne $apors arecollected on the concentrator and thenthey are desorbed into the column byre$ersing the carrier gas flow whileheating the concentrator. This process isalso called thermal desorption. Thistechni1ue allows 1uantification of lowerairborne concentrations than can bemeasured using a syringe or direct (loopin'ection. #ampling time using theconcentrator $aries from /* seconds to /*minutes and can measure concentra-



Figure 12.". Chromatogram!pictorial separation of ben>ene and toluene.(Courtesy of the ;oxboro Company.

Figure 12.#. ac=ed and capillary GC columns. (;rom The ndustrial En!ironment H ts E!aluation " Control, 4%A# Cincinnati /I6 p.

+J+.




T)BD< /+.+. Commonly Esed #tationary hases for GC

hases )pplications

#i$uid #<-6* A@-/ (methyl silicones ydrocarbons chlorinated hydrocarbonsA@-/ #<-5, (methyl!phenyl silicones )s chlorinated pesticideshydrocarbonsCarbonax +* " (polyethylene glycol olar compounds such as esters alcohols;;) #-/*** (polyethylene glycol terephthalate henols $olatile acids

Solid %&ac'ed Columns (nly)Chromosorb orapa= series (styrene! @olatile alcohols =etones hydrocarbons

di$inylben>ene polymers halocarbons (boiling points 6*-/**KC

Carbon molecular sie$es (Carbosphere L-C5 hydrocarbons#pherocarb Carbosie$eorous silica (Enibeads orasil ) L-C5 hydrocarbons

;igure /+.5. Gasoline $apor analysis on pac=edand capillary columns. (Courtesy of 4E#ystems %nc.

specific application. %n most cases columns arepro$ided by the instrument manufacturer andare described in terms of column type the

pac=ing or coating and their

dimensions (length and inside diameter.Custom si>es and pac=ings can be made forspecial sampling situations.

%n most high-end portable GCs either aconstant-temperature heated column ortemperature programming is used to enhanceseparation. Temperatures abo$e ambienttemperature increase the $olatility of the

contaminant molecules? and temperature programming which in$ol$es increasing thetemperature of the column in a predeterminedmanner as the analysis proceeds enhancesseparation of many complex mixtures becausethe lower-molecular-weight compounds mo$ethrough the column at the lower temperaturewhile hea$ier molecules begin to mo$e more1uic=ly as the column temperature is increased.

The ideal situation is to choose the operating parameters to yield sharp and narrow pea=sthat are easy to identify and 1uanti-tate for the

materials of interest. The separation is primarily dependent on the type of column andits pac=ing or coating the column length theflowrate of the carrier gas and the temperaturecharacteristics of the system. These $ariablescan be changed to achie$e optimal separationof the components in an airborne mixture butit is critical to calibrate the de$ice with a=nown gas mixture under each set of operatingconditions and then store the calibration




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data in a data library so the proper calibrationdata are used for each sample run. Ane featurea$ailable on some field GC units is the abilityto bac=flush the column to shorten theanalysis run time and also pre$ent hea$iercompounds from reaching the analyticalcolumn. Bac=fDushing re1uires two columns:a shorter pre-column and a longer analyticalcolumn. They are usually connected in serieswith a 0tee0 fitting. 3uring an analytical run

the sample is carried through the pre-columntoward the analytical column. 8hen the com-pounds of interest ha$e cleared the pre-column a $al$e arrangement switches thedirection of the carrier gas flow so it flowsthrough the 0tee0 connector to both columns.The components that ha$e already passed the'unction continue through the analyticalcolumn to the detector while compoundsbefore the 0tee0 are flushed bac= out of thepre-column and $ented. %t is important toselect the correct time to re$erse the flow

through the pre-column or compounds ofinterest may be lost or undesirable compoundsmay be dri$en through the analytical column.

Identification and Integration of Peaks.3uring this step a detector senses the presenceand amount of compounds as they elute fromthe column. Table /+.6 lists characteristics ofse$eral common types of detectors? someportable GCs feature additional detectors forspecific applications. The instrumentssoftware compares each pea= as it elutes to thecalibration data and shows the nameconcentration le$el and retention time of thecompounds identified during calibration.Compounds that are detected but which donot match compounds identified duringcalibration are listed as 0un=nowns0 and oftenmay be identified by the software bycomparing the sample analysis results withother calibration results stored in theinstruments memory or by scanning $ariouscompound libraries that may contain se$eralhundred

compounds. The compounds concentration iscalculated from the area under its pea= a stepcalled pea' integration.

#ome instruments can be programmed sothere is a delay between when the first pea=semerge from the column and when thecompound identification and pea= integration

begins. This feature called the inhibit time, ishelpful in reducing the amount of datagenerated when the initial lighter molecules

do not represent compounds of interest.

Data Display and Management. Thelaptop computer and proprietary softwarestores and displays rele$ant data such as thesample chromatogram calibrationchromatogram retention times concentrationand operating parameters. 3ata management iscritical with portable GCs because compoundidentification is based on the principle thatwhen a specific column is maintained at aspecific constant temperature and carrier gas

flow conditions the retention time of eachcompound is constant. Thus all the operating

parameters (column type temperature programming cycle carrier gas flowrate etc.must be stored along with the calibration dataso that proper identification of pea=s in actualsamples is achie$ed. )dditionally theinstrument must be recalibrated fre1uentlyand so ade1uate data storage capability isneeded to store the calibration and sampledata.

Prta$le GC I(str!"e(ts

This section describes se$eral commercial portable GC instruments that illustrate featurestypically a$ailable with this category ofinstrument.

Photovac Voyager Portable GC. The@oyager ortable GC (;igure /+.J isdesigned for en$ironmental site character-i>ation and exposure monitoring. 8eighing




T)BD< /+.6. Types of GC 3etectors

Type rinciple Compounds 3etected

;lame ioni>ationdetector (;%3

hotoioni>ationdetector (%3

<lectron capturedetector (<C3

) stainless steel burner in which hydrogenis mixed with the sample stream?combustion air feeds in and diffusesaround the 'et (burner where ignitionoccurs. The current carried across thegap of a platinum-loop collectorelectrode is proportional to the numberof ions generated by burning the sample.

4ot as sensiti$e as many other detectors.Darge linear range. &esponse is

relati$ely uniform from compound tocompound.

) sealed E@ light source emits photonswith an energy le$el high enough toioni>e the compounds in the sample. %na chamber exposed to the light sourcecontaining a pair of electrodes ionsformed by the absorption of photons aredri$en to the collector electrode where acurrent is produced that is proportionalto the concentration. Darge linear range?high sensiti$ity? selecti$ity can beintroduced by using different energylamps. &esponse $aries from compoundto compound.

Etili>es a radioacti$e source such as 6 4ito supply energy to the detector in theform of (6 radiation. %ntensity of theelectron beam arri$ing at a collectionelectrode is monitored. 8hen anelectron-capturing species passesthrough the cell the intensity of theelectron beam decreases sending out anelectronic signal. &esponse $arieswidely from compound to compound.ighly sensiti$e and selecti$e. otential

problems include excessi$e heat which

could $apori>e some of the source?0aging0 of the coated foil which must be replaced? gradual loss of the sourcesacti$ity.

)lmost all organics? response isgreatest to hydrocarbons?decreases with increasingsubstitutions of otherelements: A # Cl. 4otsensiti$e to water the

permanent gases and mostinorganic compounds.

Arganics some inorganicslower response to low-molecular-weighthydrocarbons. Can detectaliphatic aromatichalogenated hydrocarbons.)rsine phosphine hydrogensulfide. #ensiti$e to water. 4oresponse to methane.<specially good for aromatichydrocarbons.

Compounds containinghalogens cyano or nitrogroups? <C3 has a minimalresponse to hydrocarbonsalcohols and =etones.

/5 pounds it is e1uipped with an internalrefDllable carrier gas cylinder and rechargeablebattery for independent operation for up to Fhours. #ampling practitioners can $iew thechromatograms or tabular data

using the built-in DC3 or by downloading to acomputer in the field or office.+

The hoto$ac @oyager GC can be used toanaly>e air samples soil gas or the head-spaceabo$e water or soil samples. Gaseous




.10

Figure 12.$. hoto$ac @oyagerM portable gaschro-matograph. (Courtesy of hoto$ac %nc.

samples can be in'ected manually by syringeor sampled using a built-in pump and loopin'ection. Doop in'ections are ideal for fence-line ambient confined space emergencyresponse lea= detection and similarapplications. #yringe in'ections are used forapplications such as headspace analysis ofwaste streams ground water and soil extracts.The sampling practitioner can choose from amanual or continuous loop in'ection samplingmode. The instrument can be set to sample atuser-defined inter$als thereby pro$iding atime-history profile of concentration le$els forsite-specific compounds.

The @oyager uses two detectors: a pho-toioni>ation detector (%3 operating at /*.Je@ for $olatile organic compounds (@ACsand an electron capture detector (<C3. The<C3 is the most sensiti$e detector a$ailablefor the analysis of elec-trophilic compoundssuch as chlorinated

Figure 12.%. hoto$ac @oyagerM multi-column configuration allows separation of upto ,* compounds in a single sample. (Courtesyof hoto$ac %nc.

hydrocarbons and other halogen-containingorganic compounds. ) @oyager with a %3 andan <C3 re1uires ultra>ero-or >ero-gradenitrogen carrier gas. The nitrogen must beII.III pure and contain less than *./ ppmof hydrocarbon contamination. 8hen only a%3 is used the instrument can be run withnitrogen or >ero-grade air as the carrier gas.Di=e nitrogen the air must be II.III pureand contain less than *./ ppm of hydrocarboncontamination.

The instrument employs an inno$ati$earrangement of analytical columns prepro-grammed temperatures and flowrates tooptimi>e the separation of complex @AC

mixtures found in specific industries. Ane pre-column and three parallel analytical columns(;igure /+. ma=e up this configuration.Esing three separate columns allowsseparation of up to ,* compounds in a singlesample. <xcellent compound resolution on atleast one of the three column phases generallyoccurs. ) bac=fDushing feature can be used toreduce total analysis time and columncontamination by pre$enting the hea$ier0nontarget0 analytes from entering theanalytical columns.

The @oyager GC has a built-in total @AC(T@AC operational mode which allows a1uic= screen of samples for the presence of@ACs. %n a T@AC run the sample passesdirectly into the %3 without going throughthe analytical columns. %f a preset alarm le$elis exceeded a full GC analysis may be

performed to determine




which compounds are present. ) T@ACanalysis is sent through the %3 onlyHaT@AC sample cannot be run through the <C3.

roprietary software (#iteChartM ispro$ided with this instrument. The softwaresets up the preprogrammed parameters fordifferent calibration and analytical runs (calledassays) and is also helpful for data re$iew andprinting of the data including chromatogramsand tables of pea= $alues. <ach assayautomates the setup of the instrument operatingconditions and data reduction parameters

pertinent to identifying and 1uantifying apredefined set of compounds. The presetoperation parameters ensure the best separationand detection possible for the compounds in asample. The @oyagers are e1uipped withpreprogrammed assays to detect a set of targetanalytes for the following specific industries:en$ironmental (i.e. the ,* compounds on theE.#. <)s TA-/, priority pollutants list?petrochemical! refining? rubber!plastic? pulp 9paper? surfactants!sterilants? and latexpolymers. %n addition each instrument is

furnished with a uni1ue assay dis= de$elopedfrom the setup and calibration performed at thefactory to meet the users specified needs byrunning target compounds on that instrumentand sa$ing the respecti$e retention times andpea= areas in the library. The samplingpractitioner can also use the #iteChartMsoftware to set up and store additional assays.

The @oyager portable GC can be run in thefield using a personal computer with#iteChartM or using the =eypad on theinstrument as long as the desired assay hasbeen downloaded to the instrument from the

computer using the #iteChartM software. The@oyager data logs e$ery completed analysis.Ep to ,* GC log entries can be stored in theinstruments memory which is sufficient for anF-hour day based an analysis e$ery /* minutes.T@AC runs occupy less memory than GC runsso the

de$ice will typically be able to store /* timesmore T@AC runs than GC entries. Ance thememory is full the data may be downloaded orelse deleted from memory so that additionalruns may be performed. <ach GC recordincludes a complete pea= report andchromatogram. Ance data ha$e beendownloaded to the computer they can bere$iewed by scrolling through the list ofcompleted runs then selecting analy>ing and

printing a specific chromatogram or datasummary.

Di=e all GC instruments proper calibrationis critical. 8hen a calibration run is performedthe data are stored in a library in the @oyagersmemory. The library contains the retentiontime pea= area and concentration of eachtarget analyte. 8hen a standard

preprogrammed method is changed (e.g. pressure or temperature change the retentiontimes for the compounds will shift. ) newlibrary then needs to be created to identify thetarget analytes by running the compounds ofinterest with the current method conditions and

sa$ing the retention time in the respecti$elibrary.8hile the manufacturer strongly recom-

mends that the @oyager be calibrated using acalibration mix that contains e$ery compoundin the columns library it is possible tocalibrate it using a calibration mixturecontaining only a few of the compounds.Called a ratiometric calibration the instrument

performs a calibration with each compound inthe calibration gas mixture and then calculatesthe approximate retention times andconcentrations settings for the compounds that

were not present in the calibration mixture.)fter a ratiometric calibration the instrumentscompound library is updated to reflect theactual and calculated information. #ince theapproximation may affect compoundidentification and the accuracy of thecompound concentration reported by theinstrument a ratio-metric calibration is notconsidered as good as an actual calibrationwith a =nown standard of each compound ofinterest.




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Figure 12.&. 4E "odel GC-6// ortableGC can analy>e gases li1uids and soilextractions using a $ariety of columns anddetectors. (Courtesy of %3 )naly>ers DDC.

HNU Model GC-311 Portable GC. T'ismicroprocessor controlled portable instrument(;igure /+.F can analy>e gases (ambient airheadspace stac= samples process gases etc.

li1uids (water sol$ents and either headspaceor li1uid extractions of solid samples such assoils. %t has a heated in'ector for manualin'ection of gases or li1uids and has dualdetector capability chosen from sixinterchangeable detectors: hotoioni>ationdetector (%3 flame ioni>ation detector(;%3 electron capture detector (<C3 flamephotometric detector (;3 thermalconducti$ity detector (TC3 or far ultra$ioletabsorbance detector (;E@3. The instrumentis pro$ided with 4Es proprietary softwarecalled ea=8or=sM for 8indowsN

Chromatography #oftware for datamanagement and control of the GC.6

)nalyses can be run in series withnondestructi$e detectors such as %3 or;E@3 or in parallel with the other detectors toimpro$e or $erify compound identification. )built-in concentrator!thermal desorber isa$ailable as an option for indoor air 1ualityand fenceline measurements where $ery lowle$els (ppb to ppt are to be measured.

The instrument features a large o$en so

any manufacturers columns can be used. Theo$en can be operated at a constanttemperature (isothermal or with temperature

programming to increase temperature as thesample run progresses (up to +**KC for fasteranalysis or analysis of $olatile organiccompounds (@ACs and semi-$olatile organiccompounds such as poly-nuclear aromatichydrocarbons ()s some pesticides and

plastici>ers in the same sample. Typical

columns that are used include:

• &ac'ed Columns. /!,0 /!F0 or /!/J0(micropac= +-6 meters in length with6**-5** plates per meter. The typical

pac=ing material is porous polymer li1uid phase (/-6 on diatomite.

• Capillary columns. *.56- *.6+- *.+*-*./5-mm column with li1uid phase

bonded to the fused silica? a$ailable infused silica-lined stainless steel with theli1uid phase bonded to the silica?

efficiency O/***-6*** plates!m withtypical length /5-6* meters.

Sentex Scentograp P!US II. T'e Scen(tograph DE# %% from #entex #ystems %nc.is designed to operate as a portable unit or in afixed location (;igure /+.I. %t is capable ofanaly>ing air soil and water samples withconcentrations ranging from parts-per-trillion(ppt to percent ( le$els. This isaccomplished by combining different ways ofsample introduction with different types ofdetectors. #amples can be analy>ed by directon-column in'ection using a concentrator orusing a sample loop./

The detectors offered are micro argonioni>ation detector (")%3 argon ioni>ationdetector ()%3 electron capture detector(<C3 thermal conducti$ity detector (TC3and the photoioni>ation detector (%3. The)%3 is sensiti$e to organic compounds ha$ingioni>ation potential of //. e@ or lower. Thesecompounds include the halomethanes and




Figure 12.). The #centograph DE# %% field-portable GC unit. (Courtesy of %nficon %nc.

haloethanes carbon tetrachloride and ///-trichloroethane which are poorly detected byother common field detectors. This detector iscapable of detecting these compounds as wellas other hydrocarbons down to ppb le$els. The")%3 is a smaller more sensiti$e $ersion ofthe )%3. %t is ideal for use with capillarycolumns and detects organic compounds tobelow / ppb le$el. The instrument can containtwo detectors at any one time? howe$er onlyone can operate at a time. The operatingtemperature can be set between 6* to /IKC? atemperature abo$e 5*KC is recommended foroptimum performance.

The internal carrier gas cylinder is filledwith argon (II.III pure for the )%3 orhelium (II.III pure for the <C3 %3 or

TC3. The carrier gas cylinder will allow aminimum of F hours of operation and is easilyrefilled. %t is also e1uipped with an internalcalibration cylinder which supplies gasdirectly to the instruments internal calibrationsystem. Calibration gas from the internalcylinder flows through a regulator directly tothe sample loop or concentrator duringcalibration. The calibration cylinder is easilyrefillable and pro$ides a minimum

of F hours supply of calibration gas. There isalso a calibration port that is used to calibratefrom a sampling bag headspace of an externalcontainer or other external source at ambient

pressure.The #centograph DE# %% can use the

following methods to identify and 1uantifycomponents in samples:

• Esing current calibration data which is based on direct calibration Peither single point or multipoint (up to 5 pointsQ with

certified standards for up to ,F chemicals.3uring analysis the instrument comparesthe retention times obtained with those ofthe calibration run. 8hen there is a matchthe name of the compound and the calcu-lated concentration le$el is displayed onthe monitor. ea=s with no match areidentified as 0un=nown.0 This method isthe most accurate and is identical to thatused in laboratory gas chromatographicanalysis.

• Esing pre$ious calibration informationstored in data files which is similar to the

pre$ious method with the exception thatthe calibration data is recalled from thesystems memory for comparison to theanalysis data. ;or example suppose acalibration run was performed undercertain parameters and the $alues werestored in the instruments memory. %f ananalysis is conducted at a later time underthe same parameters it is possible to recallthe pre$ious calibration and compare itwith that analysis. %f there is a match the

pea=s will be named and their con-

centrations will be determined.• Esing a computer library search which is based on the assumption that those relati$eretention times of compounds separated ona column remain unchanged pro$ided thatthe operating conditions of the analysis are=ept the same. 3uring an analysis run thesystem will first 0loo=0 for compounds




.8.

that were defined in the calibration run.0Enmatched0 compounds are thenscreened using data stored in differentinternal libraries. The library searchmethod is a con$enient procedure foranalysis. owe$er library $alues must bechec=ed fre1uently in order to maintaintheir accuracy. The #centograph DE# %%can contain se$eral libraries (i.e.databases each containing up to ,F

compounds.

The instrument uses menu-dri$en softwareto control its operation process its data andstore its chromatograms. The systems can beoperated manually or set to analy>e andcalibrate at chosen inter$als storing the resultson dis= or hard dri$e for future re$iew. )detachable laptop computer controls theoperation and pro$ides the data system. Theproprietary #entex software operates the GCand collects stores and processes data.

Typical (peration. The operation of anyportable GC depends on the features of theinstrument and the manufacturers instructions.) typical operating se1uence for portable useof the #centograph DE# %% is as follows/:

/. @erify that the batteries are fully charged by charging o$ernight particularly after a prolonged period of nonuse.

+. Turn on the carrier gas $al$e and thecalibration gas $al$e (if the internalcalibration cylinder is to be used at thecalibration source. @erify that both gas

cylinders are full by inspecting the pressure gauges when $al$es are opened.&efill cylinders if needed before fielduse.

6. %f calibration from an external source isdesired the internal calibration cylindergas $al$e should be turned off. Theinstrument will automatically draw asample through the external calibration

port.

,. %nspect the column pressure using thecolumn pressure gauge. )d'ust column

pressure if necessary. Typical operating pressure should be +*-6* psi for pac=edcolumns and F-/5 psi for capillarycolumns.

5. Connect the &#-+6+ connector from theinstrument to the computer turn on thecomputer and start the software program.The computer will automatically powerthe GC unit initiate the start-up cycleand display rele$ant parameters and

prompts.

J. #elect the calibration or analysis mode asappropriate. Change parameters selectfeatures as re1uired and manipulate dataas prompted by the computer.

. 8hen using direct syringe in'ection ofsamples use these guidelines:

• as Samples. #ample $olumes up to

+cc can be in'ected. ) gas-tight syringeshould be used for handling thesamples. The syringe needle should be++-+J gauge with either a ++K be$el

point or a side port tip. The $olume to be in'ected is dependent on the sampleconcentration. The higher the sampleconcentration the smaller the samplein'ection $olume must be to a$oido$erloading the detector. ;or sampleconcentrations between 5** and 5***

ppm a sample si>e of *.5 cc or lessshould be used. %f sample concentrationis un=nown start with a smaller si>ein'ection. %ncrease the in'ection $olumeto increase the analysis sensiti$ity. ;orthe lower ppm range (/ to /*ppm anin'ection si>e of / cc can be used. arts

per billion (ppb analyses of gassamples would re1uire a samplein'ection of up to +cc.

• #i$uid Samples. The sample si>e ismuch less than that used for a gas




sample in'ection typically ,uD or lessdepending on the sample concentration. Thecapacity of the syringe should range

between luD and /* uD and it should ha$e a++-to +J-gauge needle with either a ++c be$el

point or a side point tip. F. )fter usefollow the computer

prompts to shut down the instrument.8hen the instrument is not in use itshould be connected to the charger atall times.

Prta$le GC Mai(te(a('e a( Use

%n addition to the material already co$ered inthis chapter there are se$eral maintenance anduse considerations for portable GCs. &outinemaintenance in$ol$es steps such as:

• &eplacing in'ection port septum e$ery +-5in'ections.

• &eplacing inlet filter approximatelyonce!wee= depending on sample dustcontent.

• Cleaning E@ lamp window as needed.• &eplacing E@ lamp when needed.

• Cleaning in'ection port as re1uired.

• Conditioning column when changingcolumn or if contamination is suspected.

• urging internal carrier gas cylinder beforeshipping instrument or if cylinder becomescompletely empty.

)ny column can become contaminated withcompounds ha$ing long retention times. %fcontamination of a column is suspected

installing a new column is one way to chec=.Contamination may be pre$ented by using thebac=fDushing feature if a$ailable or reducedby flushing the column with carrier gas for aperiod of time after e$ery analysis. owe$er adisad$antage of purging the column after eachanalysis is the time in$ol$ed since it willdecrease the

number of samples that can be analy>ed in aday. ;or a contaminated column simpleflushing may be used or ba=ing the column ina drying o$en at a temperature recommended

by the manufacturer while passing nitrogen oranother gas through the column. The ba=ingtime and temperature depends on the type ofcolumn being cleaned.

8hen changing columns a conditioning period is re1uired. %f the ends of the columnha$e been =ept capped during storage thelength of conditioning time is reduced. 8hen

installing the column a$oid touching theunprotected column ends as contaminationmay result.

)lthough portable GCs ha$e extensi$e data-logging and data management capability it isusually helpful to =eep a separate record of =eyinformation. ;igure /+./* shows typicalinformation elements to be recorded for use ofa portable GC instrument.

%t is also important to consider theappropriate shipping regulations concerningcompressed gases if a sur$ey is planned at a

distant location. Generally it is best to ha$ecarrier gas and calibration gas cylindersshipped to the sur$ey location ahead of time or

purchased locally since there are manyrestrictions on shipping compressed gascylinders.

Stra#e Re!ire"e(ts

roper storage of portable GCs is importantand the re1uirements $ary depending on howsoon the instrument should be ready for use.;or example one manufacturer gi$es thesestorage guidelines+:

• "aintain a flow of carrier gas through thecolumn to pre$ent contamination. ;orlonger storage periods connect theinstrument to an external supply of carriergas.

• 3o not allow the internal carrier gascylinder to empty completely to

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PORTA3LE GASC4ROMATOGRAP4S*GCs-

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Figure 12.1*. G

data sheet.




pre$ent contamination of the internalcylinder and columns. %f the internalcylinder empties completely it must be

purged before refilling. The column mustthen be flushed and the instrument must

be allowed to warm up for 6* minutes. The baseline of the instrument must beallowed to stabili>e before it is ready foruse. #tore the instrument in a location thatis free of $olatile organic $apors and gaseswith ambient temperature between 6+K;and /*5K;. %f the battery has beendischarged connect the instrument to the)C adapter and recharge the battery. ;orimmediate a$ailability the following stepsare recommended: Dea$e the instrumentturned on. Calibrate once e$ery +, hours.Connect the instrument to a carrier gascylinder or refill the internal cylindere$ery J-F hours.

Connect the instrument to the )C adapterwhen not in use. ;or a$ailability within 6*minutes: Turn instrument off. Connect it to

an external cylinder of carrier gas.Connect it to the )C adapter. To use theGC turn it on and allow a 6*-minutewarm-up period. Then calibrate it beforeuse. ;or a$ailability o$er a longer period:;ollow the storage recommendations for6*-minute a$ailability but let theinstrument stabili>e for at least /+ hours

before calibration. This will result inoptimum performance.

NIOSH Method for Ethylene O!de ByPort"#le GC

Ane established method using a portable GC is4%A# Manual of Analytical Methods(4")" 4umber 6*+,:

ProcedreF. #et up a portable GC with a %3 using

the following parameters: column R /.+m x 6 mm A3 T;< pac=ed withCarbopa= BT ,*!/** mesh. Carrier gasflow rate R /5ml!min. )lso assemble

portable computer or integrator batterycharger regulator and any other

peripherals necessary for indi$idualinstruments. )llow the instrument towarm up and e1uilibrate for 6* minutes.

I. Chec= the sampling e1uipment to

pre$ent contamination. Ese differentsyringes for sampling and for standard

preparation. %dentify each syringe with auni1ue number. #egregate bags used forsample collection from those used forcalibration standards.

/*. Calibrate the GC daily in the field.repare bag standards by adding a=nown $olume of ethylene oxide to a=nown $olume of clean air in a bag. Byadding a =nown $olume in S*.D to aspecified number of liters of air a =nown

concentration in ppm will be created. *ote+ Because ethylene oxide is aflammable gas the shipment of thecompressed gas must comply with,IC;& //-/ regulations regardingshipment of ha>ardous materials.

//. <$acuate a 5-D to /*-D bag completely by drawing the air out with a large /-D to+-D syringe.

/+. 3raw clean air (or oxygen or nitrogenfrom a supply cylinder into the syringefor measured transfer into the bag.

)lternately if a clean air supply is nota$ailable draw room air throughcharcoal sorbent into the syringe. &epeatuntil the bag contains 5 D of air.

/6. )dd a =nown amount of pure ethyleneoxide or standard ethylene oxide mixtureto the bag by means









.88

of a gas-tight syringe. Example+ Esing agas-tight syringe ta=e 5* uD from acylinder of pure ethylene oxide and in'ectit into 5D of air to create a /*-ppmstandard. )lternately +** uD of a +$!$ ethylene oxide mixture (e.g. FF!/+w!w ;reon /+ and ethylene oxide can beadded to the 5 D of air to obtain a /*.F-

ppm standard.

/,. )llow the bag to e1uilibrate withoccasional =neading for at least 5minutes.

/5. )naly>e ali1uots of $arious si>es toestablish a calibration graph. ;or each

point three replicate samples should bedone. ;or example using a highinstrument attenuation (low sensiti$ityin'ections of *.+mD *., mD *.J mD *.FmD and /* mD might be possible. Theseamounts would correspond to in'ectionsof +iiD ,iiD JiiD FiiD and %AT%D. An amore sensiti$e attenuation in'ections of

*.*+ mD *.*, mD *.*J mD *.*F mDand *./* mD would be typical. &esultswill $ary from instrument to instrumentand from time to time on the sameinstrument.

/J. lot iiD of ethylene oxide $ersus pea=height or area if the GC cannot do thisautomatically. This plot should be astraight line.

/.eriodically throughout the day chec= thecalibration by repeating some of these

in'ections. %deally each sample would be brac=eted before and after within'ections of standards although thissituation is seldom practical. #ome GCsare capable of doing automatic periodiccalibrations with programming.

/F.Collect samples by drawing air from thecontaminated area directly into a syringeor filling bags for an integrated T8)sample.

/I.;or syringe sampling draw air directlyinto a gas syringe. Collect

syringe samples by first purging a gas-tight syringe se$eral times with clean airto remo$e any residual ethylene oxidefrom pre$ious samples? then draw air intothe syringe at the time and location ofinterest. %f larger syringe samples aredesired such as +* mD of air it will benecessary to transfer some of the sampleto the smaller syringe being used in thechromatograph. %t is essential that the

si>es of all grab sample in'ections be thesame if concentrations are to becompared. ) rubber cap placed o$er theend port of the larger syringe can ser$e asa septum for the smaller (5** uDsyringe.

+*. ;or integrated air samples for T8)determinations a clean bag of plastic orother material must first be e$acuated. )

personal air sampling pump is used at thehighest airflow a$ailable.

+/.)ttach the plastic bag $ia tubing to theoutlet of a personal sampling pump and

pump air from the contaminated area intothe bag at a rate calculated to fill the bago$er the sampling period. This rate will

be between +* mD!min and 5** mD!min.Terminate sampling before the bag isF* full. The pumps flow rate must bewithin 5 of the initial settingthroughout the sampling period.

++.)naly>e the bag sample within + hoursafter completion of the sampling tominimi>e loss of analyte by adsorptionand permeation as follows: ;ill a gas-tight syringe purged se$eral times withsample from the sample bag. Then emptyit to the desired $olume and in'ect that$olume into the chromatograph with a1uic= firm motion. &ecord the number ofthe syringe. Ese replicate analyses todetermine the repeatability of theanalysis. %f no




estimate of concentration is a$ailable use anin'ection $olume /* uD to +5 ixD at a highattenuation to reduce the possibility ofcolumn and detector o$erload. 3ependingon the results of this in'ection larger $ol-umes and!or more-sensiti$e attenuationsmay be selected. /J. Calculate theconcentration of eth-ylene oxide from thecalibration graph (riD and the in'ection$olume (mD:

uD(gas iiD ppm R--------R------H-

D gas mD

I(ter&reti(# Meas!re"e(ts with thePrta$le GC

)s noted pre$iously it is possible for morethan one compound to ha$e the same retentiontime and in certain circumstances whereun=nowns may be present it will mean that apea= appearing at or near a gi$en retentiontime is not /** confirmation of a gi$encompounds presence. owe$er if the

instrument is operating properly a lac= ofpea=s will usually mean there are nocompounds present at the detection le$el of theinstrument. The best way to confirm thepresence of a gi$en compound is to collectadditional samples for analysis in thelaboratory on a GC with two differentcolumns each of which is capable of resol$ingthe mixture of interest and doing se1uentialanalyses. )s this is difficult to do in mostportable GCs where the results are1uestionable bag samples should be collected

and ta=en to a laboratory for analysis. Theinterpretation of a chromatogram re1uires theuse of calibration reference data that ha$e beengenerated through testing.

Sources o" #rror. 8hen using a GC foranalysis there are se$eral sources of error thatmust be understood and a$oided in

order to yield accurate results. Theseinclude/+:

• ea= integration errors that are due to problems in starting or stopping the pea=integration by the instrument or computersoftware. The potential problems include

baseline noise interfering (co-eluting pea=s or excessi$e tailing of the pea=s ofinterest. These errors can occur somewhatrandomly and cause different integrationsfor consecuti$e runs for the same con-

centration of a specific contaminant underthe same operating conditions. Because ofthis potential for error it is important forthe sampling practitioner to re$iew thechromatograms for ob$ious errors and toreintegrate where necessary using different

parameters to achie$e accurate results.

• #yringe in'ection techni1ues may cause alarge 0trailing pea=0 on the chromatogramthat is not due to a target compound. %f anin'ection pea= is obser$ed it may beeliminated by setting the inhibit time oneor two seconds longer than the retentiontime indicated for this pea=.

• #ampling errors occur when the analyticalsample entering the instrument is differentfrom the airborne composition andconcentration that exists at the samplingsite. This can be due to reasons such asnonstandard syringe sampling andin'ection techni1ue contaminants not

being completed des-orbed when aconcentrator is used or contaminantscondensing or otherwise absorbing on thewalls of Tedlar sampling bags or in

sampling lines. Careful attention tosampling techni1ues including the use ofheated sampling lines and bags whereneeded along with rigorous laboratorye$aluation of planned sampling techni1uescan help to identify and reduce samplingerrors.









of the cur$ed detector. The ions reaching eachcollector plate are 0counted0 as electricalsignals.

"# sometimes pro$ides a better means ofidentifying specific compounds using a libraryof data de$eloped for the specific instrumentthan do other GC detectors. ) GC!"# isespecially useful when compounds emerge atthe same time from the GC column (co-elutedespite efforts to ad'ust operating parametersto obtain good separation or for identifyingun=nown compounds since the spectrographic

pattern of the un=nown pea=s can be comparedto information in the built-in data library.

GC!"# instruments ha$e long been used inthe laboratory but their use as portable fieldde$ices is relati$ely new. They gi$e thesampling practitioner new options but arecostly and complex to operate. They probablyadd the most $alue when cost sa$ings or otherbenefits result from ha$ing real-timeinformation in the field and a GC or other less

complex

instrument will not suffice.The )#%T< by %nfDcon (;igure /+./+ is

a portable GC!"#. %t weighs about 65 poundsand contains many of the features discussedearlier for portable GC instruments such astemperature programming and an optionalconcentrator for $ery low le$el air samples. %tuses nitrogen as a

carrier gas and has an internal calibration gascylinder. %t has se$eral built-in programs toma=e field use more con$enient. Ance thesampling practitioner selects a method theinstrument automatically ac1uires and analy>esthe sample. The instrument monitors critical

parameters thereby $erifying the tuning of the"# and mixing internal standards with thesample at the re1uired ratios. &esults can beshown on the instruments display panel andstored for later downloading to a computer.The instrument can be used in two modes5:

• #ur$ey mode where 'ust the "# is used togi$e 1uic= 1ualitati$e and semi1uantitati$eresults. This mode is good for screeningsamples e1uipment lea= chec=ing orfugiti$e emissions testing. 8henconcentrations exceed preset thresholdle$els an alarm sounds.

• )nalytical mode which combines the GCand "# techni1ues. This permits detailedanalysis of samples and it is good forfollow-up when the instrument in the

#ur$ey mode detects a compound ofinterest.

Typical applications of the )#%T<include source testing for en$ironmental

permits ha>ardous waste site testing andemergency response testing. %t is findingincreasing use for response to terrorism e$ents?a third-party manufacturer ma=es a )#%T<0simulator0 that is designed for training withthe instrument without using the consumablesupplies such as carrier and calibration gas./

IN$RARE% (IR)SPECTROPHOTOMETERS

8hen infrared (%& radiation is passed througha sample of gaseous molecules the


Figure 12.12. T e %n con )#%T<is a portable GC!"# weighing 65

poun s t at r ngs new capa ty to







NFRARED *IR-SPECTROP4OTOMETERS

.95

gas absorbs some specific wa$elengths of theinfrared radiation. This increases the energy ofthe gas molecules and so their $ibration orrotation increases. %& generally is that portionof the electromagnetic spectrum from * nmto /*** 'am. %n %& spectroscopy the terma!e number is also used This is the numberof wa$es in one centimeter and is thereciprocal of the wa$elength so %& rangesfrom about /+I** cm/ to /* cm0/. Enli=e

%3s and similar ioni>ation detectors theenergy of the %& source is not high enough tocause ioni>ation of the gas molecules. %nsteadthis energy transfer from the infrared radiationto the gas molecules can be seen as either (aincreased energy (temperature in the gasmolecules compared to molecules that ha$enot been exposed to the %& radiation or (bdecreased intensity of some wa$elengths ofthe %& radiation that is transmitted through thegas sample.

Two characteristics ma=e %& a good method

of identifying and measuring theconcentration of certain compounds:

• %& absorption spectrum is uni1ue to eachgas or $apor molecules so %& can be afairly specific detection method. Table/+., shows the %& absorption bands bychemical group and Table /+.5 lists theabsorption wa$elengths for chemicalstypically measured using %& technologyalong with the lower detection limit.

• The amount of %& absorbed is directlyrelated to the number of the gas moleculesin the sample which gi$es a goodmeasurement of concentration. %ncreasingthe length of the %& path through thesample allows measurement of lowconcentrations. %nternal mirrors aregenerally used to increase the path lengthto /* meters or more a sample cell ofreasonable dimensions.

)lthough the absorption spectrum is uni1uefor each chemical care must be

TABLE 12.#. Specific nfrare+ Absorption

Ban+s

)bsorption

Grou in Band im

)l=anesC6 HCH HC+R 6.65-6.J5

)l=enes HCRC+ 6.+5-6.,5)l= ne

HCRCH 6.*5-6.+5)romatic 6.+5-6.65#ubstituted aromatics J./5-J.65)lcohols HA +.F*-6./*)cids HCAA 5.5-J.**)ldeh des HCA 5.J*-5.I*Uetones ,c-o 5.J*-5.I*<sters HCAA& 5.5-J.**

Chlorinated HCHCl /+.F*-/5.5*Source+ 4%A#: The ndustrial

En!ironment, ts E!aluation " Control.

ta=en to select the optimum wa$elength fordetection. ;or example Trichloroethyleneexhibits three absorption maxima (;igure/+./6 which occur at /*.5F //. and /+.F

'am. Theoretically any one of these could be

used to detect this compound but the /*.5F-um pea= o$erlaps with ;reon-//6N and so isnot suitable if ;reon could be present and the/+.F-um pea= o$erlaps with water $apor

pea=s. Therefore the //.-um pea= is usuallythe best for trichloroethylene measurement.

%& instruments $ary widely in complexityand functionality. #impler de$ices arededicated to a single contaminant while morecomplex instruments can measure manycompounds by scanning the %& spectrum andapplying sophisticated mathematical analyses

to the raw data. )s an illustration an %& at ,.6 'am is commonly




TABLE 12.. Typical Analytical /a0elengt' an+ inimum etectable

Concentration for 3 nstruments

Compound 8a$elength (Sim "inimum 3etectable Concentration (ppm

)cetaldeh de I.+J)cetic acid F.+)cetone F.,F)cetonitrile I.JF)ceto henone /*.*)cet lene 6.*5)cet lene tetrabromide F.II)cr lonitrile /*.J

)niline I.56Ben>aldeh de F.5FBen>ene0 I.I6Ben> l chloride I.5,Bromoform F.IJ/ 6-Butadiene //./*Butane /*.,*But l acetate F.66V-But l alcohol I.*Carbon dioxide ,.+Carbon disulflde ,.*Carbon monoxide ,.JCarbon tetrachloride /+.JCellosol$e acetate F.FIChloroben>ene I.,*Chlorobromomethane F.6IChlorodifluoromethane I.+*Chloroform /6./+Cresol F.FFCumene I.I*C clohexane 6.,/C clo entane //.,*3iborane 6.F6m-3ichloroben>ene I.,o-3ichloroben>ene /6.55

-3ichloroben>ene I.6*

/ / -3ichloroethane I.5*/ +-3ichloroeth lene /+.6*3ichloroeth l ether I.*53ieth lamine F.II3imeth lacetamide /*./*3imeth lamine F.I3imeth lformamide I.6J3ioxane I.*J<nflurane F.IJ<thane /+.+*<thanolamine /+.I6<th l acetate F.6+<th l alcohol I.J<th l ben>ene I.I*<th l chloride /*.5*

/./ *.6 *.J.J *.6 /.J/.+ *.J *.5*.+ *.6 +.++.5 *., 6.I5./ *.J *.6

/*.+ ,.F +./*./ *.6 *.,/.5 /./ /./*.+ +.6 *.I.* *.J *.6*.J +.5 *.,5.6 *.*I/./ *., /.+*.+ *.6*.*6

/*.J +.I+./ +.6 6.*6.,




.9.

TABLE 12.. Continued


<th lene /*.*<th lene dibromide F.JF<th lene dichloride F.6<th lene oxide 6.6*<th l ether I.*6;ormaldeh de 6.5J;ormic acid I.6J

;reon // /*.IJ;reon /+ I.6*;reon /6B/ F.5,;reon +/ I.5*;reon //+ I.I*;reon //6 F.*;reon //, F.Jalothane /+.,Je tane 6.,*exane 6.6I dra>ine /*.J dro en c anide 6.*6%soflurane F.F,

%so ro l alcohol F.I,%so ro l ether I./+"ethane .*"ethox flurane /+./*"eth l acetate I."eth l acet lene 6.*"eth l acr late F.5"eth l alcohol I.*"eth lamine 6.6J"eth l bromide .J*"eth l cellosol$e I.J+"eth l chloride /6.5I"eth lene chloride /6.,"eth l iodide 6.6J

"eth l merca tan 6.6F"eth l methacr late F.F*"or holine I.+*

4itromethane 6.64itrous oxide ,.JFActane 6.,*entane 6.6Ierchloroeth lene //./*hos ene //.IFro ane 6.6ro l alcohol I.J*ro lene oxide /+./J

ridine I.I*#t rene //./*

*.5 *.J/.6 *.+.F *.5*.+

//.+ *./*., +.6

/+.F 6., /.

*.6 6.5 6.I*.J /.*.*, /.5,./ /.* *.++.6 +.* *./*. /.I +.6*.6 6.*

/*.* /.F/.5 /.**. *.I,.5 *.,*.6 ,.J*.+ *./J.5 *.F

/./ F.J*.5




TABLE 12.. Continued


#ulfur hexafluoride /*.F*/ / + +- F.J*Tetrah drofuran I.,*Toluene /6.FITotal h drocarbons 6.6I/ / / -Trichloroethane I.6I/ / +-Trichloroethane /*.I*Trichloroeth lene /*.F,

@in l acetate F.,+@in l chloride //.6*@in lidine chloride I.,*W lene /6.+*

/.I*.*+/.,*.JI.+6.I/.+*.I*.,*./*.F*.6+.*

0 "inimum detection le$el exceeds current permissible exposure standard?therefore recommended for gross lea= detection only.

Analytical a!elength+ The analytical wa$elength is usually the strongest bandin the spectrum that is free from interference due to atmospheric water andcarbon dioxide. The listed wa$elengths are approximate. %f more than one %&-absorbing material is present in the air in significant concentration the use ofanother analytical wa$elength may be necessary.

Minimum detectable limit+ The concentration that would produce an absorbancee1ual to twice the pea=-to-pea= noise in a typical portable %&.

Figure 12.1". %nfrared spectra of trichloroethylene. (;rom The ndustrial En!ironment H ts E!aluation " Control, 4%A# Cincinnati /I6 p.

+6,.

used to measure carbon dioxide (C*+ le$elsduring indoor air 1uality (%)L studies and inthe brewing food processing and miningindustries. %n %)L in$estigations an increase ofC*+ abo$e the ,**-5** ppm in normal ambientair indicates that there is too little outside airbeing introduced in the occupied space for thenumber of people present. %n breweries C*+ isproduced as part of the fermentation processand le$els may exceed accept-

able exposure le$els in enclosed areas around$ats. ;igure /+./, shows a typical infraredinstrument that pro$ides continuous auto-ranging detection of C*+ from le$els /* ppm toJ by $olume (J**** ppm and features

pea=!hold memory an internal sampling pumpand optional datalogging. ) dedicated %&instrument is also $ery good for measuringcarbon monoxide (CA since there is littleinference by other gases at ,.J 'am.




.9

;igures /+./5 through /+./ show different%& instrument configurations. ;igure /+./5 isa basic layout with a single cell. %n somedesigns the sample is allowed to diffuse intoand out of the cell rather than ha$e discreteinlet and outlets for a pump-dri$en system.This configuration has no way to ad'ust forpossible drift in the %& source or detector.;igure /+./J is a single cell configuration withtwo detectors. The acti$e filter!detector is

chosen to measure

Figure 12.1#. %nfrared-based carbon dioxidemonitor pro$ides auto-ranging detection of

le$els from lAppm to J****ppm. (Courtesyof %ndustrial #cientific Corporation.

the compound of interest while the referencefilter!detector is selected to ignore the targetcompound. %n actual operation the referenceside pro$ides the >ero point while the acti$eside pro$ides the signal for measuringconcentration. This arrangement ad'usts forchanges in the %& source and it also has thead$antage of doubling the effecti$e pathlength since the %& beam tra$els to the mirrorand then bac= to the detectors.

;igure /+./ shows a popular design withtwo cells. ;or instruments dedicated to asingle chemical the reference cell can either(a contain pure target gas and ser$e as the

baseline for total absorption or (b contain pure reference gas (such as nitrogen andser$e as the >ero baseline. ;or instruments thatmeasure more than one gas the reference cellis filled with a pure reference gas. ) chopperwhich is a dis= with slots in it alternatelyallows the light beam to pass through thesample and reference cells to the single

;orall %&

instrumentsthe type ofdetector isimportant tomeasuring

low le$els of

Figure 12.1$. 3iagram of a two-detector infrared detector configuration.

(Courtesy of %nternational #ensor Technology.

Figure 12.1. 3 agram o a s mp en rare etector. Courtesy o




(Courtesy of %nternational #ensor

Technology.

contaminant. ) $ariety of designs exist that arebased on measuring temperature rise as the %&beam hits the detector(s or as the temperatureof the gas sample in the sample cell increasesdue to %& absorption. 3ifferent approachesinclude: (a thermoelectric detectors orthermisters that directly con$ert heat into anelectrical signal (b microfDow sensors or adiaphragm between the detectors in thereference and sample cells to measure the

small decrease in pressure in the detectorchamber due to absorption of the %& radiationtransmitted through the sample cell. Ane no$elapproach is called a photo-acoustic detectorwhich uses a sensiti$e microphone to measurethe increase in pressure within a fixed samplecell due to the absorbed %& radiation.

Typical applications for %& instruments inaddition to en$ironmental measurements andoccupational exposure monitoring include:

• ndoor Air uality Studies. "easurementsfor compounds such as C*+ CAformaldehyde or organic $apors.

• ume /ood0Tracer as Analysis. Ane ofthe standard tests for laboratory hood

performanceF is to release a tracer gaswithin the hood under different operatingconditions and monitor the hood perimeterfor lea=age bac= into the laboratory. )

portable %& can measure commonly

used test gases such as sulfur hexaflu-oride(#;J.

• Emergency 1esponse Analysis. 3eter-mining airborne le$els of ha>ardous spillsand releases and ma=ing realtime decisionsregards personal protecti$e e1uipment forresponders boundaries of 0safe0 >ones andthe need for community e$acuation orshelter-in-place.

• #ea' detection. )round e1uipmenthandling ha>ardous chemicals such asmedical anesthetic gases or process unitsas part of routine operations or pre$enti$emaintenance.

IR I(str!"e(ts fr Meas!ri(# Ma(% Gasesa( Va&rs

%nfrared instruments with the capability ofmeasuring the concentration of many gases and$apors differ from the configurations shown in;igures /+./5 through /+./ in that they need away to $ary the wa$elength of the %& radiationdirected through the sample cell to match theabsorption spectra of target compounds. Thiscan be achie$ed by a $ariable wa$elength filteror by ha$ing se$eral fixed-wa$elength band-

pass filters in the de$ice. %n addition theseinstruments need a means to $ary the pathlength using ad'ustable mirrors or anothermeans in order to achie$e ade1uate sensiti$ityfor different compounds and also increase themeasurement range for certain compounds.


-





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.98

Figure 12.1&. The "%&)4 #apph%&e portableinfrared instrument. (Courtesy of Thermo<lectron Corporation.

MIRAN SapphIRe Analyzer. O(e of themost common %& de$ices for field mea-surements is the "%&)4 #apph%&e series ofinstruments (;igure /+./F from Thermo

<lectron Corporation. The #apph%&e )naly>eris a$ailable in three models with gascalibrations from one to o$er /** gases. %t is amicroprocessor-controlled single-beaminstrument that utili>es interacti$e pro-gramming to prompt the sampling practitionerthrough a$ailable options and functions.

The %& wa$elength is $aried using a $ari-able filter from . to /,./ 'am along withse$en fixed band-pass filters: /.F 6.6 6.J,.*,.+,.5 and ,. 'am.The sample is drawninto the +.+6-D sample cell by an internalpump at a rate of /5 D!min. The path length

can be $aried between *.5 and /+.5 m. )fterthe instrument is powered up and stablesample analysis time is +* seconds minimumand 6 minutes maximum. The response time isapproximately /F seconds to reach I* offinal reading. The #apph%&e has a digitalreadout of concentration in $arious units(ppm percent and mg!m6 or absorbance units()E. There is a &#-+6+ connection to use apersonal computer for operating theinstrument and downloading data althoughthe de$ice can

also be operated from the alphanumeric=eypad. The de$ice weighs +, pounds and

battery ser$ice life is approximately fourhours. Because %& de$ices are sensiti$e toambient temperature relati$e humidity (&and atmospheric pressure three differentoperating conditions are specified:

• &eference operating conditions withinwhich the influence of temperature &

and pressure is negligible is +6 +KC 5* /* & and /,.-/5.6 psi.

• 4ormal operating conditions withinwhich the de$ice is designed to operate atthe specified accuracy is 5-,*K C 5-I5& (noncondensing and /+.5-/5.6 psi.

• 4ormal operati$e conditions withinwhich the de$ice can be sub'ected without

permanent impairment of operatingcharacteristics is /-5*KC *-/** &(noncondensing and //.J-/5.Ipsi."aximum temperature for intrinsically

safe models is ,*K C.

&ourier 'rans"orm In"rared (&')I$* +nal,er. The ;ourier transform infrared (;T-%& de$ice is a more complex and powerfultype of analy>er when compared to a simple%& analy>er discussed abo$e. The ;T-%& uses aunit called a "ichelson interferometer tomeasure the absorption of %& radiation atdifferent wa$elengths. The interferometer(;igure /+./I functions as follows: &adiationfrom the %& source is split into two e1ual

beams in the beam splitter. Ane beamcontinues on a straight path to a mo$ingmirror while the other beam is deflected at anangle to a fixed mirror. 8hen the two beamsrecom-bine after being reflected from themirrors they undergo a process calledinterference. %f both reflecting mirrors areexactly the same distance from the beamsplitter both beams will be in phase with eachother and the resulting recombined beam outof the unit will ha$e the maximum amplitude.The




Figure 12.1). 3iagram of a ;ourier transforminfrared (;T-%& analy>er. (Courtesy of%nternational #ensor Technology.

position of the mirror is computer controlled? alaser precisely measures the position of themirror. ;or each fre1uency as the mo$ingmirror mo$es through its cycle theinterference pattern of the recombined beamwill be from totally in phase to totally out ofphase to totally in phase again.

Esing a beam chopper the recombined beamalternati$ely passes through the sample celland the reference cell to reach the detector. Thecomputer collects the data from the detectorwhich is a complex measurement of all thephase relationships at a gi$en time to producean interfero-gram, which shows the intensityof the infrared radiation as a function of thedisplacement of the mo$ing mirror. ) sophis-ticated computer program applies amathematical ad'ustment called a ;ouriertransform to the interferogram to determinethe identity and concentration of the gases that

are present. ;or a multicompo-nent analysisthe computer retrie$es calibration data in thecomputers library and tries to calculate aspectrum that is a close match to the actualsample spectrum by mathematically $aryingthe concentration of each component. 8hen itachie$es the best possible fit between thecalculated spectrum and the sample spectrumit reports the results.



Figure 12.2*. Temet Gasmet 3W-,*/*portable ;T-%& analy>er ready for field use.(Courtesy of Temet %nstruments Ay elsin=i;inland.

The G)#"<TM 3W-,*/* from TemetCorporation is a ;T-%& de$ice designed for on-site measurements (;igure /+.+*. %tincorporates ad$anced hardware and softwareto pro$ide a portable high-speed identificationand 1uantification of multiple gaseouscompounds simultaneously and accuratelywith results a$ailable in seconds forapplications such as:

• <n$ironmental emissions monitoring

• Luality control

• 8or=place air monitoring

The instrument can analy>e up to 5*compounds simultaneously. The sample isdrawn into the /.*-D sample cell by aninternal pump at a rate of l-5D!min. ) filter (+

'am is re1uired on the sample line to protectthe optical parts from particulate matter. Thesample cell has a multipass fixed path lengthof /.+ +.5 5.* or I.Fm. )fter the instrument is

powered up and









.90

stable sample analysis time is /+* seconds orless depending on the gas flow andmeasurement time. )n external personalcomputer controls the instrument. Theproprietary software called C)DC"<TM isused to compute the concentrations and errorlimits of the different components present inthe sample gas. The reference spectra neededfor the analysis are stored on the fixed dis= ofcomputer and are loaded from the library

when used in the analysis of an un=nownsample. )n &#-+6+ connection connects thecomputer to the instrument./*

The 3W-,*/* uses an interferometer calledthe Temet Carousel interferometer. TheCarousel interferometer is rugged andwithstands the demanding en$ironmentalconditions of nonlaboratory en$ironment. TheCarousel interferometer modulates the infraredradiation coming from the infrared source asdescribed abo$e. The modulated light passesthrough the temperature-controlled sample

cell. The transmitted infrared radiation isdetected by a thermoelectrically cooleddetector.

%t is recommended that the instrument isoperated in the following en$ironmentalconditions:

• *-,*K C operating temperature inshort-term use

• /5-+5KC operating temperature inlong-term use

• I* relati$e humidity at +*KC

noncondensingThe ambient temperature of the use location

should be stable. Temperature fluctuations of afew degrees Celsius can in some cases affectthe analysis results and the accuracy of themeasurements decreases. The influence of thetemperature fluctuations can be eliminated byremea-suring the bac=ground (>ero spectrumat the existing ambient temperature. )ddi-tionally the use location should be free ofstrong $ibrations. The standard case is not

explosion-proof and so the 3W-,*/* must not be used to measure explosi$e gas mixtures orgases that might form an explosi$e gasmixture with the ambient air.

!dvantages and "imitations. Thead$antage of %& is that units can be purchasedthat are specific for gi$en chemicals ortunable units can be purchased and used formany different compounds with a minimum of

setup time. %n the field they are easy to useand pro$ide stable operation.

3etection limits depend on the absorptioncoefficient of the compound at a gi$enwa$elength or fre1uency. The limit of detec-tion for many compounds is in the range oflppm to +*ppm. "aximum concentrations arecommonly in the low percent range.

The usefulness of %& analy>ers for mon-itoring complex mixtures is limited becauseo$erlapping pea=s produce an additi$eresponse ma=ing concentrations appearhigher than they actually are. ) wa$elengththat is relati$ely uni1ue to a chemical isselected for monitoring and ideally thereshould be no others that interfere. owe$erthis is often not the case and a re$iew of thechemicals li=ely to be present duringmonitoring should be done to assure that aninterferent will not be a problem. %nterferencesdepend on the contaminant being measured.;or example chlorinated hydrocarbons will allabsorb at approximately the same wa$elength.This problem can be partially minimi>ed byta=ing measurements at a secondary

absorption wa$elength for substanceconfirmation. ) primary interferent is water$apor. The effect of water $apor can beminimi>ed by passing the air sample throughsilica gel or a similar drying agentmaintaining constant humidity in the sampleand calibration gases by refrigerationsaturating the air sample and calibration gasesto maintain constant humidity or usingnarrowband optical filters in combination withsome of the other measures.// Carbon dioxidecan also be an interference




although its effect at concentrations normallypresent in ambient air is minimal. )ccording tothe )merican #ociety for Testing and "aterials()#T" 5* ppm of carbon dioxide may gi$ea response e1ui$alent to *.5 ppm carbonmonoxide.// #ome instruments ha$emicroprocessors that allow them to correct tosome degree for interferences and thesophisticated mathematical algorithms in a ;T-%& de$ice can correct for many interferences.

Calibration. A multipoint calibration is

re1uired when an analy>er is first purchasedwhen the analy>er has had maintenance thatcould affect its response characteristics orwhen the analy>er shows drift in excess ofspecifications as determined when the >ero andsingle point calibration is performed. ) >eroand single point calibration is re1uired beforeand after each sampling period or if the ana-ly>er is used daily. The fDowmeter should becalibrated as well when the analy>er if firstpurchased when it is cleaned and when itshows signs of erratic beha$ior.//

Ance calibration plotting cur$es are pre-pared for a gi$en compound air concentrationscan be obtained by measuring the absorbanceat the analytical wa$elength and reading theconcentration from the point where theabsorbance intersects the cur$e. "ostcalibration cur$es of this type will ha$e somecur$ature so it is best to use a plot preparedwith three or four data points rather than usinga single-point and a straight-lineapproximation. %f only a single calibrationconcentration is a$ailable it may be used? themeasurements will be most accurate near this

concentration point and less accurate at other$alues due to cur$ature.

"anual calibration of most long path-length%& instruments is done using a closed-loopsystem. #mall amounts of contaminant(typically microliters are added to a fixed$olume sample chamber (generally +-J Dwithout measurably affecting

the pressure of the system creating a =nownconcentration in the parts per million (ppmrange. Eser calibrations re1uire considerable

practice in using the closed-loop system and becoming familiar with the instrument in orderto consistently generate reliable accuratecalibrations. Calibration of %&s can also bedone using =nown concentrations in gascylinders.

Care must be ta=en during calibration of%&s because these are nondestructi$einstruments? thus any contaminant that enters

the instrument will come out essentiallyunchanged allowing the user to be exposed tothe calibrant gas. The exhaust from theanaly>er should be $ented to a laboratory hoodor other exhaust to remo$e contaminant bothduring calibration and analysis to pre$ent

buildup in the surrounding en$ironment.The first step in setting up an %& analy>er to

measure a gas is to select the wa$elength and path length. 8a$elengths are chosen tomaximi>e analytical sensiti$ity whileminimi>ing interferences from other $apors

commonly present in the wor=place oratmosphere where this contaminant is typicallyfound. ;or example if measuring styrene$apor in a chemical plant where acrylonitrile

butadiene styrene ()B# polymer ismanufactured then /6-butadiene is li=ely to

be present. #ince this compound absorbs at themost fre1uently chosen analytical wa$elengthfor styrene (ll.lAum an alternati$ewa$elength must be chosen. An the other handif doing a sur$ey in a fiberglass boat hullconstruction facility where acetone iscommonly used as a cleaning sol$ent for

styrene the acetone $apors would not be aconcern as they are not li=ely to ha$e anyabsorption pea=s at wa$elengths that wouldinterfere with styrene.

#ince ambient air always contains water$apor and carbon dioxide the analyticalwa$elengths selected must reflect this ma=eup.#ome gases ha$e a limited number








INFRARED *IR-SPECTROP4OTOMETERS

.05

of possible analytical wa$elengths andoccasionally a wa$elength must be chosenwhere water $apor can interfere. This situationis associated with the 5- to F-um region wherestrong water $apor absorbance occurs. Toreduce the interference of any water $apor theinstrument should be 0>eroed0 with air that hasabout the same humidity as the sample.

%f an %& is o$erloaded from being exposedto too high a concentration inaccurate

calibrations and negati$e or suppressedreadings at certain concentrations can result. %fthe absorbances for any of the calibrationstandards go abo$e one absorbance unitswitch to a shorter path length or use a wea=erabsorption band.

There are many compounds for which %&scan be used. %n the case where the instrumenthas not already been set up to monitor for agi$en compound the manufacturer can oftenpro$ide information to select appropriatewa$elengths and path lengths for setting up

%&s to monitor many different gases and$apors. 8hen the path length in a $ariablepath length instrument is changed theinstrument should be recalibrated.

Closed-#oop Calibration for the 1. 8henusing the closed-loop techni1ue the userintroduces pure samples through a septumwith a li1uid or gas syringe. The sample iscirculated through the system by means of theclosed-loop pump. Esing the closed-loopsystem for the calibration of organiccompounds with low $apor pressures mayresult in errors due to adsorption on the wallsof the closed-loop system. The results of usinga calibration cur$e based on these data wouldbe to o$erestimate concentration duringsur$eys. Therefore e$en though closed-loopcalibration systems are not recommended forcompounds with $apor pressures less than/5mmg (+5KC from the standpoint of usingthe instrument the errors may not besignificant in certain types of sur$eys./+

Procedre/. 3etermine the sample $olume

re1uired for the desired concentration limit. ;or gases the $olume to bein'ected is calculated using

i ppm R H 2 3

where 2i 4 $olume of gas to be in'ected2 3 4 $olume of closed-loop calibrationsystem.

;or li1uids (at atmospheric pressureand +5KC the $olume to be in'ected iscalculated using

@i(d( +,.,5 xlA6 ppm R------------------

M2 3

where 2i is the li1uid sample $olume in

uD d is the li1uid density in g!mD M isthe molecular weight 2 3 is the $olume ofclosed-loop calibration system in D and+,.,5 x /*6 is the number of uD of $apor

per millimole of analyte at normaltemperature and pressure (4T.

+6. %ntroduce clean air into the samplingchamber using a >ero air cylinder orroom air drawn through a >eroingcartridge.

+,. Connect tubing from the 0out0 con-nector of the closed-loop pump to the

input port of the analy>er. Connect tubingfrom the 0in0 connector of the pump tothe 0cal port0 connector of the analy>er.Turn the sample $al$e to the 0calibrate0

position.

+5. Turn on the closed-loop pump.

+J. %n'ect the 1uantity of calibrant gas orli1uid needed to fill the sample cell withthe desired concentration. %n'ect e1ualincrements to co$er a full range ofconcentrations. ;or example if themaximum concentration is +** ppm




and the number of calibration points is to be fi$e then each in'ection shouldincrease in concentration by ,*ppm.;re1uently replace the sili-cone rubberdis=s called septa, used in the in'ection

ports of closed-loop calibration systems.)fter a number of in'ections they may notreseal properly.

+. ;or each concentration input the le$elinto the instruments memory or otherwiseset the 0span0 control (depending on thespecific instrument. #ome instruments

automatically fit a calibration cur$e to thedata points.

+F. ;or instruments with a 0general purpose0 scale (not mar=ed in ppm prepare a plot of meter reading $ersusconcentration with meter reading on the yaxis and concentration on the x axis.En=nown concentrations can then befound using this cur$e and the meterreading.

+I. ;ollowing calibration with eachchemical flush the closed-loop system

and cell with clean air or nitrogen.

The microprocessor capability of manyinstruments has simplified calibration in thatcertain parameters are programed into theinstrument at the factory to allow for anelectronic calibration chec=. The internalelectronic calibration system often allows forfield calibration without the need forcalibration gas which is sufficiently accuratefor performing screening samples. )lthoughthis automatic (factory-pro$ided calibration

sa$es time it is not as accurate a calibrationwith a standard.

&ield /peration. There are three primary typesof sampling modes for %& analy>ers: bagsampling lea= or fugiti$e emissions testingand continuous monitoring. %n bag samplingdiscrete breathing >one area or

process samples can be collected in bags asdescribed in the chapter on sample collectionde$ice methods for gases and $apors (ChapterJ using personal sampling pumps. The flowrate of the sample pump is not critical as longas it is constant o$er the duration of thesample. ;ollowing sample collection the bag istransported to the location of the %& analy>erwhere it is connected to the inlet of the samplecell. )n internal or auxiliary pump pulls thesample from the bag through the samplingchamber where it displaces the ambient air.

8hen the instruments response to the samplein the bag reaches a maximum a reading ista=en. The concentration of the contaminantcan be determined from comparing the plot ofinstrument response $ersus the calibrationcur$e concentrations or directly from thereadout if it is in ppm. ) similar application isto collect exhaled breath in bags and analy>e iton the %&.

Bags can also be analy>ed to identify the presence of un=nowns on %&s with scanningcapabilities. The scan of the un=nown

atmosphere is compared with a scan of con-taminants expected to be present to see if anyunidentified pea=s are present. The instrumentshould generally be connected to a personalcomputer to manage the data during thisanalysis.

8hen sampling in situations where theatmosphere is un=nown one techni1ue is tooperate the %& at 6.,'am (the C- bondstretching fre1uency using the maximum

possible pathlength. %n the field the responseunder these conditions should be reported ase1ui$alents of whate$er compounds ha$e been

used to calibrate the instrument o$er thedesired concentration range using the closed-loop method./6

%n sur$ey instruments designed to detectlea=s an extended sample probe of up to J feetin length made of inert tubing with a dust filterattached is used to ma=e spot measurements atmany different locations such as door sealssumps lines and fittings. %f the filter becomesclogged the sampling




.0.

flow rate will decrease resulting in a slowerinstrument response. &eplace the filtercartridge when the response time hasincreased noticeably or after ,** hours of use.

%n continuous monitoring the instrument isstationed to collect samples at a location ofinterest. ) pump continuously draws sampleinto the sample cell and the absorbance iscontinuously displayed on the instrumentreadout and stored in a data logger for printout

later.%f measurements exceed the range for which

the instrument was calibrated it must beremembered that the response of %& analy>ersis not linear o$er the total range of theinstrument particularly at the ends of thescale? therefore extrapolation past calibrationpoints is not ad$ised. %f much higherconcentrations than anticipated are identifiedmonitoring may need to be repeated followingcalibration at higher concentrations.

%f the process being monitored is a constant

operation with little $ariation readings can beta=en with the monitor e$ery 6* minutes. %fthe process is $ariable it may be necessary tota=e the readings as often as $ery 5 minutes orcontinuously as described abo$e.

%n compliance sampling with an %& de$icecalibration should be done using either apremixed gas in a cylinder or the closed-loopcalibration system rather than relying solelyon the internal calibration system. ;orpersonal sampling Tedlar gas bags capable ofcollecting a minimum of JD and personalsampling pumps e1uipped with exhaust portsare needed. Care must be ta=en to assure thatsufficient air is collected to ade1uately purgethe sample cell during analysis. %n certainen$ironments a drying tube Teflon samplingline par-ticulate filter or >ero gas filter maybe necessary.

%n general where ambient air is drawndirectly into the instrument all samplingshould be done with the sample hose and

particulate filter attached to pre$ent dust and particulate matter from entering the cell andaccumulating on the mirrors and windowsthus interfering with the performance of theinstruments by increasing bac=ground le$els.

%&s should be used outdoors with great care because cooler temperatures and humidity cancause condensation on the mirrors andwindows. %f the instrument has been in a colden$ironment condensation may ta=e place in

the cell if the sample is drawn into it beforethe instrument has warmed up properly. %f themirrors do become fogged permanently high

bac=ground readings can result. #ome mirrormaterials are more susceptible to humidity.;or example sodium chloride windows cloudmore easily than those made of sil$er bromide.The mirrors on some instruments can be

periodically cleaned. The cell ports in %&sshould be co$ered with protecti$e plastic capswhen the %& is not in use to pre$ent dust andmoisture from contaminating the optics.

;or all uses of an %& instrument it isimportant to pre$ent corrosi$e gases and$apors that could damage mirrors or cell ordetector windows from entering the samplecell.

Xeroing %& analy>ers is a critical step. %f thesampler >eros in an atmosphere containing thecompound of interest or an interference andthen analy>es air that contains less of the samecompound a negati$e reading or 0error0message will occur. This reading can occurwhen the >ero gas filter has become saturatedor if the sampler >eros on humid air andsubse1uently analy>es air that is drier than the>ero. ) charcoal canister sometimes termed a>eroing cartridge or >ero gas filter must be

placed o$er the probe for proper >eroing. 4otethat charcoal has a limited ability to absorbwater $apor. These cartridges should be storedin a sealed plastic bag to pre$ent exposure tocontaminated atmospheres when not in use.#atu-




ration of the cartridge depends onthe nature and concentration of the contami-nants that are pulled through it. %f a newcartridge produces an appreciably loweranaly>er reading the old cartridge should bediscarded. %f an instrument is >eroed with acontaminated cartridge a negati$e $alue mayoccur when ma=ing measurements the resultbeing low $alues for all measurements becausethe ambient bac=ground readings may be lowerthan the concentration in the cartridge used for>eroing. 8hereas some sources recommend

using nitrogen for >eroing others recommendusing room air to account for normal humidityconditions./,

#ag Sample Collection for $itros %&ide'sing an I( )*

6*. #et up a portable %& analy>er to thefollowing parameters: 5 4 ,.,F-,.JF 'am

path length R *.5-,* ". )llow theinstrument to warm up and e1uilibratedfor /5 minutes.

6/. erform an on-site multipoint calibration at fi$e or more concentrationso$er the range of lAppm to /***ppm.

*ote+ Because nitrous oxide supportscombustion the shipments of thecompressed gas must comply with ,IC;& //-/ regulations regardingshipment of ha>ardous materials.Calibration for nitrous oxide canfre1uently be done using materiala$ailable on-site when sur$eys are donein hospitals dental offices and $eterinaryoperations because generally the nitrous

oxide in use is of sufficient purity.6+. Xero the instrument while recirculating

uncontaminated air through the samplecell. %f the area where the instrument is

being calibrated is ser$iced by the same$entilation system as the area to bemonitored it will be necessary to obtaina source of

uncontaminated air (or nitrogen or oxygenfor >eroing the instrument. ,. %n'ect a=nown $olume of nitrous oxide into thesample cell with a gas-tight syringethrough tubing or by using a septumattached to the sample cell. Calculated theconcentration of nitrous oxide in thesample cell:

@olume of 4>A in'ected (ul

@olume of cell

8hen the instrument reading stabili>esrecord meter or display reading.

66. repare a calibration graph of ppm(Cs $ersus meter or display reading.

6,. #elect one of the followingsampling modes according to the desiredform of the data: ambient air orintegrated air samples for T8)determinations.

65. "o$e the instrument to the firstarea to be sampled. ) probe with asample line can be used to allow more

flexibility Thus the instrument can be placed nearby and the probe can be usedto mo$e for example around the doorsof a sterili>er or held o$er the shoulderof an employee while opening the doorof the sterili>er to get a pea=measurement.

6J. ;or ambient air turn on the instru-ment pump and record the readings onthe display. %f data are to be expressed asa T8) concentration an internaldatalogging feature or a computer will

be needed to store measurements.6. ump air to be analy>ed through

the sample cell to purge the cell.Typically two to three cell $olumes arenecessary. 8hen output stabili>esrecord the reading as a measurement.


C, m R







SUMMAR;

.0

6F.Ese the calibration graph to determinethe concentration by mo$ing along thehori>ontal axis to the display readingand mo$ing to the point on the line thatcorresponds to this concentration. The

ppm $alue for this point on the line canthen be read on the $ertical axis.

6I. 3uring each days operation peri-odically rechec= the calibration byrepeating measurements with thecalibration gas at three or more points

on the graph.,*. ;or integrated air samples for T8)

determinations a clean bag of plastic orother material must first be e$acuated. %tcan be done using a personal airsampling pump at the highest airflowa$ailable.

,/.)ttach the plastic bag $ia tubing to a personal sampling pump and pump airfrom the contaminated area into the bagat a rate calculated to fill the bag o$erthe sampling period. This rate will be

between +*mD!min and 5**mD!min.Terminate sampling before the bag isF* full. The pumps flowrate must bewithin 5 of the initial settingthroughout the sampling period.

,+.)naly>e the bag sample within + hoursafter completion of the sampling tominimi>e loss of analyte by adsorptionand permeation.

I(ter&reti(# Meas!re"e(ts withI(frare A(al%<ers

"ost %& instruments express concentrationdirectly in units of parts per million (ppm orpercent. owe$er some may display results asabsorbance or percent transmission. Thepercent transmission %6T) readout is usedwith a calibration cur$e to determine theconcentration of the sample. The absorbance() scale is related to the 6 T scale by A 4-log T and is not a linear scale as is the 6 Tscale. %t too must be com-

pared to a calibration cur$e in order todetermine the actual concentration of thecompound being sampled. The calibrationcur$es must be prepared in ad$ance using thesame control settings (path lengthwa$elength slit width which will be usedduring measurements and the instrumentcalibrated immediately prior to sampling toassure the cur$e is still $alid.

SUMMAR;

This chapter describes direct readinginstruments that can identify and measure theconcentration of specific compounds in anairborne mixture which are gas chro-matographs (GC GC!mass spectrometers(GC!"# and infrared (%& instrumentsincluding fourier transform %& (;T-%&. Thereare also many %& de$ices that emit only onewa$elength of %& radiation and this arespecific to one airborne compound (e.g. CA

and C*+? these are co$ered in detail in thischapter as part of the o$erall discussion of %&instruments.

The instruments that can determine theconcentrations of specific compounds in anairborne mixture are high-end de$ices that areexpensi$e and sophisticated and can becomplicated to operate. Generally they ha$ethese characteristics in common: )ll aredesigned to be used with a personal or laptopcomputer? they are not designed to identify thecomponents of a completely un=nown or0mystery0 airborne mixture since they must becalibrated with the specific compounds theyare measuring? and because of their si>e andcomplexity they are used for area or sourcesampling rather than routine personaloccupational exposure measurements.

8hen selecting between a portable GC or%& instrument for field measurements twoimportant factors to consider are:

• %& de$ices re1uire less time to completean analysis than do GCs. Ten




minutes for a CG run is typical while +minutes or less is typical for an %&instrument reading. • GCs ha$e a lower limitof detection for most compounds (in the ppbor ppb range than do %& instruments (in the

ppm range.

"a'or de$elopments with this category ofdirect reading instruments has been theincrease in functionality due to more powerfulmicroprocessors and introduction of ad$ancedinstruments such as the portable GC!"# and

;T-%&. The sampling practitioner should staycurrent in direct reading technology to ensurethat they are aware of the latest ad$ances whenselecting instruments for their specificsampling needs.

RE$ERENCES

,6. Scentograph &#7S (perating Manual. ;airfleld 42: #centex #ystems%nc.

,,. 2oyager &ortable as ChromatographTraining Manual. 8altham "): hoto$ac%nc.

,5. /*7 Model C-899 &roduct nformation. 8alpole "): rocess)naly>ers DDC.

,J. 4ational %nstitute of Accupational#afety and ealth. *(S/ Manual of

Analytical Methods %*MAM:), Method8;<3, ,th ed. ". <. Cassinelli and . ;.AConnor eds. 3# (4%A# ublicationI,-//6 )ugust /II,.

,. /A&STE= &ortable C0MS &roduct nformation,n/con,%nc.<ast #yracuse4Y.

,F. 1adiation and Chemical /a>ardSimulation H /A&STE=. Duton EnitedUingdom: )rgon <lectronics.

,I. Chou 2. /a>ardous as Monitors, A &ractical uide to Selection, (perationand Applications. 4ew Yor=: "cGraw-ill+***.

5*. )merican #ociety of eating&efrigeration and )ir Conditioning<ngineers Standard 99<-9??@ H Method ofTesting &erformance of #aboratory ume

/oods, )tlanta: )#&)< /II5.5/. M1A*: Sapph1e= &ortable

Ambient Air Analy>er nstruction Manual("% J//-*6. 8altham "): Thermo<lectron Corporation.

5+.ASMET= 5-B<9< (perating Manual.)ustin TW: )ir Luality )nalysis %nc.

56.)merican #ociety for Testing and"aterials: "ethod 36/J+. hiladelphia:)#T".

5,.#ammi B. #. Calibration of "%&)4 gasanaly>ers: <xtent of $apor loss within aclosed loop calibration system. A/A .,,(l:,*-,5/IF6.

55.uide to &ortable nstruments for Assessing Airborne Contaminants at /a>ardous Daste Sites. Gene$a#wit>erland: 8orld ealth Argani>ation/IFF.

5J.De$ine #. . et al. )d$antages and disad-$antages in the use of ;ourier transforminfrared (;T%& spectrometers for monitor-ing airborne gases and $apors of industrialhygiene concern. A/A . ,(:/F*-/F/IFI.

5.4ational %nstitute of Accupational #afetyand ealth. *(S/ Manual of Analytical

Methods %*MAM:), Method <<, ,th ed.". <. Cassinelli and . ;. AConnor eds.3# (4%A# ublication I,-//6)ugust /II,.



CHAPTER 1&

COLORIMETRIC S;STEMS FOR GAS AND VAPOR

SAMPLING

This chapter co$ers direct-reading de$ices thatrely on color change to measure airborneconcentration of chemicals. These de$ices fallinto three main categories:

• 3etector tubes and similar products forshort-term or grab samples.

• Tubes (either with a sampling pump or passi$e and badge-li=e units or 0spot plates0 for long-term measurements.

• <lectronic instruments that collect airsamples on a mo$ing tape or in a li1uid andthat report the airborne concentration basedon the reaction between the target chemicaland the reagents in the tape or li1uid.

<ach type of colorimetric system representsuse of appropriate technology to fill a specificapplication for the sampling practitioner.

3etector tubes are probably the oldest direct-reading de$ice still in use and are a con$enientway to rapidly sample for ,**-5** differentgases and $apors. 8hen long-termcolorimetric de$ices were

introduced they filled a gap because theyallowed longer-duration measurements than the0grab0 sample with standard detector tubes.)lthough long-term tubes ha$e probably beendisplaced somewhat by personal-si>e electronicchemical-specific instruments with data-loggingfeatures they are still a good way to sample for

some common contaminants and wherechemical-specific electronic sensors do not exist.Colorimetric electronic instruments are mainlyused in applications where an electrochemicalsolid-state or other direct-reading sensor is nota$ailable.

Colorimetric de$ices operate on two broad principles: %n length of stain de$ices theconcentration is related to the amount (length ofreagent that is discolored whereas with colorintensity de$ices the concentration is related tothe degree of color change as compared to a

standard. "ost detector tubes are length of staindesign but badges and other products are often based on color intensity readings. ;or $isualreading of results length of stain

Air Monitoring for Toxic Exposures, Second Edition. Byenry 2. "c3ermott %#B4 *-,/-,5,65-, 7 +**,2ohn 8iley 9 #ons %nc.


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.08



.09 COLORIMETRIC S;STEMS FOR GAS AND VAPOR SAMPLING

de$ices are generally considered preferable to

color change units since color charts can fadewith time or not pro$ide realistic colorcomparisons and there is wide $ariation inhuman perception of color./ Aptical readinginstruments are pro$ided with some colorintensity detectors as a means of impro$ingaccuracy.

)ll colorimetric de$ices ha$e temperaturerelati$e humidity and ambient pressure limitsas specified by the manufacturer. Aften both anormal range (which is the range o$er whichno correction from the manufacturer-pro$ided

calibration is needed and a maximumoperating range (which denotes the outsidelimits where calibration correction factors canbe applied are specified. )dditionally somecolorimetric de$ices such as tape samplersneed some moisture in the air in order tofunction and so it is critical to follow themanufacturers specification? a relati$ehumidity of ,* is a typical re1uirement forthese instruments. Di=e all monitoringprocesses colorimetric systems are sub'ect tointerferences from nontarget chemicals that canresult in either high or low erroneous readings.%n some cases the colorimetric technology haseliminated interferences that pre$ent the use ofother monitoring techni1ues thus ma=ingcolorimetric methods the preferred samplingapproach. The sampling practitioner muste$aluate possible interferents when selectingthe appropriate sampling method for anyairborne contaminant.

%ETECTOR T'BES

3etector tubes are used for short-termmeasurements often termed grab samples.They pro$ide the ability to do direct-readingmeasurements while in the field for a wide$ariety of gases and $apors. #ince nolaboratory analysis is re1uired they pro$idefast on-site results and are often consideredalong with direct-reading elec-

Figure 1".1. iston-style pump for detectortubes. (Courtesy of 4extte1 DDC.

tronic instruments when immediate results areneeded. The primary use for these de$ices isfor occupational sampling since they are notsensiti$e enough to detect the low le$els ofcontaminants needed for en$ironmentaldetection.

They function on the principle that specificsampling media change color whencontaminated air is pulled through them and

they ha$e been a$ailable for J* years or longer.) typical sampler is a glass tube filled with asolid granular material such as silica gel thathas been coated with one or more detectionreagents that are especially sensiti$e to thetarget substance and 1uic=ly produce a distinctlayer of color change (;igure /6./. Table /6./lists some typical reagents used inside thetubes for different gases and $apors. )calibration scale is printed on the side of thetube which is used to read concentrations ofthe measured substances (gases and $apors

directly when both ends of the tube are bro=enoff and a specified $olume of air is drawnthrough the tube using a hand-powered pump(typically either of 0piston0 or 0bellows0design or a battery-powered pump. %n the casewhere a tube can be used for differentconcentration ranges there may be two scaleson a tube each corresponding to a differentnumber of stro=es of the grab sampling pump.

%t is important to note that there is a wide$ariety of tubes a$ailable that contain



DETECTORTU3ES

.00

T)BD< /6./. Color-Change &eactions in #elected 3osimeter Tubes

Gas "easured &eaction Color Change

Carbon monoxideydrogen sulfide#ulfur dioxideydrogen cyanide

CA U +d(#*6+ H F d C*+ U +#*6 +# b(C6CAA+ H F b# +C6CAA #*+ BaCl+ +* H F Ba#*6 +C/ C4 gCl+ H F g(C4+ +C/

YellowHblac=- brown 8hiteHdar= brown GreenH yellow YellowHred

Source+ &oberson &. 8. et al. erformance testing of #ensidyne!Gastec 3osiTubes for CA +# #*+ and C4. A/A Conf. &resentation, "ay +//IF5.

different chemicals and operate on differentreaction principles. The information in thischapter is intended to be a generalintroduction to this type of air monitoringsystem. Alays refer to the instructions for thespecific tube(s being used for accurateoperating and safety information. Themanufacturers instructions for the specificdetector tubes are included as an insert in thetube box and they are critical to proper use ofthe tubes. #ome manufacturers also publish amore comprehensi$e handboo= or manual fortheir tube systems. &ead these for informationon interferences and relati$e standardde$iations for each tube as well as the numberof stro=es time between stro=es and timenecessary for color de$elopment temperaturehumidity and atmospheric pressure effects.The literature also describes the function ofeach layer in the tube which is helpful inidentifying possible interferences if unan-ticipated color changes occur. Ather $aluable

information is any special precautions such as:whether the tube may emit smo=e or heat upduring use? whether the tube re1uires oxygenor airborne water $apor for proper reactions tota=e place? whether a tube with no readingafter a test can be reused for anothermeasurement? if the tube must be held in acertain position (i.e. $ertically upward forproper operation? and proper disposalprocedures for used or out-of-date tubes.

There are se$eral different types of tubesdepending on the target chemical (;igure



;igure /6.+. 3etector tubes are a$ailable for awide $ariety of toxic chemicals. (Courtesy of4extte1 DDC.

/6.+. #imple tubes ha$e 'ust one reagentwhile others ha$e a mixture of se$eralreagents. ;or some contaminants the tubecontains a prelayer before the color

de$elopment layer to either (a remo$einterfering compounds such as moisture orcompounds similar to the target compound or

(b otherwise condition the target compoundfor analysis. ;or example the prelayer mayreact with the gas or $apor of interest tocon$ert it to a different chemical that can bemeasured by the detecting








722 COLORIMETRIC S;STEMS FOR GAS AND VAPOR SAMPLING

reagents. The prelayer in tubes detecting

ben>ene is usually designed to remo$e tolueneand xylene because these compounds wouldalso react with the detecting layer due to theirsimilarity in structure to ben>ene.

Ather gases and $apors are not $ery reacti$eand thus need to be reacted with $ery powerfulchemical reagents to brea= down thesenonreacti$e compounds into other more readilydetectable substances. These powerful reagentsmay be contained in a separate tube connectedin series or in a li1uid-filled ampoule withinthe main detector tube that is bro=en 'ust

before use to coat the granules with a reacti$ereagent. )n example is the 3raeger tube fortoluene diisocyanate which is a long tube withtwo separate ampoules co$ered with plasticand an indicating layer. %n these situations it isimportant to follow the specific se1uenceindicated in the manufacturers instructions andalso practice with the tubes before attemptingmeasurements in the field. The portion of thetube containing the ampoule is bent gentlyuntil the ampoule brea=s while it is pointing inthe right direction so the reagent reaches thecorrect layer.

<ach tube has a specified concentrationmeasuring range that can often be 0expanded0by $arying the $olume of the sample throughad'usting the number of hand pump stro=esthat are drawn. This feature may also allow anad hoc ad'ustment when the extent of the colorchange either exceeds or does not reach thecalibration scale(s printed on the tube. ;orexample when the length of color change doesnot reach the calibration scale additionalsampling stro=es can be ta=en (up to aspecified maximum until the stain interface

extends into the calibration >one. %n this casethe true concentration is determined bydi$iding the tube reading by the ratio of thepump stro=es ta=en to the number of stro=esspecified in the instructions. #ometimes thisinformation is pre-

Figure 1".". Bellows-style pump for detectortubes. (Courtesy of 3raeger #afety %nc.

sented as 0correction factors0 in the tubesinstruction sheet. 8hen the color change layerexceeds the calibration scale because ofhigher-than-expected concentration repeat thetest with a fresh tube and sample with half ofthe standard $olume. %f the color change layerstays within the calibration scale the tubereading should be doubled to determine the

true concentration.There are two different types of pumpsa$ailable: the piston $ariety (;igure /6./ andthe bellows type (;igure /6.6. <achmanufacturer has its own design and man-ufacturing techni1ues. ;or example some

piston-type pumps use orifices to control flowrate while other piston-type pumps use only theresistance of the granules pac=ed in thedetector tube to limit flow rate. ) pump withmultiple sampling orifices will accuratelycontrol both the $olume of air sampled and therate of airflow during a test. The specificmanufacturers instructions for each tube willlist the re1uired orifice setting and the $olumeof air re1uired for each tube as well as thetime re1uired to pull that $olume through thetube. Bellows-type pumps utili>e the tube

pac=ing for resistance. "any bellows pumpdesigns ha$e a chain that is taut when the

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Figure 1".%. 3raeger C"#M (chipmeasurement system uses an optical sensor todetect color change in reagent-filled chips.

(Courtesy of 3raeger #afety %nc.

senses the color change and shows theconcentration reading on the instruments DC3display? a data recorder is also a$ailable.Currently chips are a$ailable for about /different chemicals.

=!alit% C(trl

The most important elements of 1uality control

in detector tube manufacturing are the purity ofthe reagents used grain si>e of the gel oradsorbent method of pac=ing the tubesmoisture content of the gel uniformity of thetube diameter and proper storage precautionsto preser$e the shelf life.+ recision accuracyand reproducibil-ity $ary with the ageconditions of storage and lot-to-lotmanufacturing of these tubes. Grain si>e of thecoated granules in the

tubes may $ary among tubes and within tubes.

) fine grain si>e is said to pro$ide a uniformdistribution of airflow through the tube alongwith sharp demarcation lines.6 8ithin a gi$entube $ariations in particle si>e can lead tostriations in the stain and cause a poorlydefined (fu>>y stain line.

To ensure a high precision indication gasdetector tubes are carefully manufactured to (aha$e =ey dimensions (such as inner diametermaintained within strict limits (b control theairflow resistance of the filling reagents and

pac=ing material and (c pro$ide detection

reagents with long-term stability. The tubesundergo stringent 1uality control tests:%ndi$idual production lots are tested andcalibrated to ensure the highest calibrationaccuracy for each lot. The certification

program described below is an important1uality control effort for the limited number oftubes co$ered by the program.

Dete'tr T!$e A''!ra'%

The typical accuracy specification for detectortube systems is +5 when the reading iscompared to a =nown gas standard at theoccupational exposure concentration. Thisspecification was established by 4%A# intheir certification program conducted between/I6 and /IF6 and has been continued as anexpectation for these de$ices. 8hile otherdirect-reading instruments may be a$ailablethat are more accurate there are se$eralconsiderations to =eep in mind when 'udgingdetector tube accuracy and suitability for use:

• 3etector tubes re1uire no user calibration

o$er their listed shelf life which is usuallytwo years or more. 3irect-readingelectronic instrument generally re1uireregular calibration often a daily span gasexposure.

• 3etector tubes are also designed to wor= ina wide array of en$ironmental conditionsfrom * to ,*KC and at least



DETECTORTU3ES

72

/* to I* relati$e humidity. Correctionfactors are supplied o$er the specifiedtemperature and relati$e humidity range.Aften a direct-reading electronicinstrument has a narrower allowabletemperature and humidity rangeassociated with the specified instrumentaccuracy.

)lthough the 4%A# certification program

was discontinued in /IF6 a similar programwas implemented in /IFJ by the %nternational#afety <1uipment %nstitute (%#<% andcontinues today based on )merican 4ational#tandards %nstitute!%nternational #afety<1uipment )ssociation ()4#%!%#<)#tandard /*+., The program includes ane$aluation of both the detector tubes andsampling pump used by each system andtesting is done for pump $olume accuracy andlea=age as well as system accuracy. The tubesare exposed to a specified concentration of test

gas and then a six-person team analy>es eachtubes corresponding length of stain.;ollowing certification a manufacturer canuse the #<% certification mar= on the product.Ender both the 4%A# and #<% programsdetector tubes are tested by an independentlaboratory and must meet an accuracy le$el of+5 at test le$els of / + and 5 times the)CG% TD@7 Gthreshold limit !alue) and65 at half of the TD@7 all at a I5confidence le$el. The #<% program is limitedto tubes in the TD@ range and to about +,listed substances so by design the certificationdoes not co$er all detector tubes.

%n addition to the #afety <1uipment%nstitute (#<% certification program fordetector tubes international bodies ha$eissued standards regulating the properties ofdetector tubes for measuring airbornecontaminants such as the 2apanese %ndustrial#tandard %nstitution (2%# U*F*, British#tandard %nstitution (B#56,6 3eutsches%nstitute fur 4ormung or the German #tandard%nstitution (3%466F+

and the %nternational Enion of ure and)pplied Chemistry (%E)CHerformance#tandard for 3etector Tubes. Table /6., listssome testing parameters from these standards

bodies.%n one study tests were performed to

compare the accuracy of +# CA C*+ andtoluene detector tubes from $arious manu-facturers. The tests were conducted by themanufacturer sponsoring the study and by

three independent laboratories. <ach type oftube was tested using the piston or bellowshand pump from the matching manufacturer.)ll pumps tested passed the specification of+ lea=age after + minutes with a sealedtube inserted. Gases were filled into a Tedlar

bag from a 4%#T-traceable standard cylinder(/*-5* ppm +# 5*-,** ppm CA /** ppmtoluene and *.+-/* C*+ and a sample$olume drawn according to the manufacturersspecification. )ll tubes ga$e similar readingswithin /5 of the standard gas $alues. The

results are well within the industry norm ofZ+5 accuracy5

Accuracy 2ersus &recision. 8hen reading themanufacturers literature for detector tubes itis important to distinguish between accuracyand precision information. The accuracy of adetector tube system (or any measurementsystem is the le$el of agreement between thesystem and a =nown standard in this case atarget gas of =nown concentration. The

precision of a measurement $alue is the le$elof agreement between it and other

measurement $alues obtained under the sameconditions. "any detector tube handboo=s andspecification sheets lists a standard de!iationfor each tube on the indi$idual data sheet(which often is less than +5 but the stan-dard de$iation is a measure of precision.#pecifically standard de$iation is anindication of how far a group of repetiti$emeasurements is expected to stray from thea$erage of all the measurements. This iscompletely independent of accuracy: ) box



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DETECTORTU3ES

728

of detector tubes could display a $ery smallstandard de$iation (i.e. $ery good precisionif all tubes read about the same $alue in a testatmosphere e$en if the $alue was not close tothe actual concentration./

The concept of standard de!iation can beexplained by recalling that two types of errorscan occur with de$ices such as detector tubes:

• &andom errors are slight fluctuations

in readings compared to the actualconcentrations that occur with tubesystems meeting manufacturing specifications that are used according todirections. The fluctuations are due to$ariations in inner diameters of detector tubes in densities of fillingreagents in sensiti$ities of reagents or in the sampling practitioners who readthe tubes. To e$aluate random errorsthe relati$e standard de$iation is usedwhich shows in percentage how the

reading de$iates from the mean $alue.This $alue is also called the coefficient of !ariation (C@:

&elati$e standard de$iation (C@#tandard de$iation

R-------------------------x /**"ean $alue

• #ystematic errors are due to non-random causes such as a lea=ingsampling pump incorrectly calibrateddetector tubes improper samplingtime inappropriate storage or usage of detector tubes or presence of interfer-ents. The concept of standard de!iationor C2 does not apply to systematicerrors.

Intercangeabilit, o" 'ubes and Pumps "rom0i""erent Manu"acturers. T'ere has been anongoing contro$ersy for many years aboutwhether it is acceptable to use onemanufacturers tubes with a hand or otherpump from a different $endor. An

one hand the pragmatic approach says thatonce the total sampling $olume and flowratefor a gi$en tube is specified it is unimportanthow that air is drawn through the tube. %n factmany ad hoc sampling arrangements ha$e

been de$eloped such as the multi-tubesampling manifold for ha>ardous waste sitesdescribed later in this chapter that expand theutility of these tubes and their contribution to

protecting wor=ers. The opposing $iew applies

mainly to the tubes certified as part of the #<%or a similar process: %t states that the tube and

pump are tested and certified as part of a0system0 and so it is not permissible tosubstitute unappro$ed e1uipment in theappro$ed system. %n particular flowrate is animportant parameter since it determines theabsorption rate for the chemical reactionsoccurring in the detector tubes to produce thecolor change and length of stain.

The inad$isability of interchanging tubesand pumps was clearly restated in the latest

$ersion of )4#%!%#<% #tandard /*+-/II*(&eaffirmed /IIF,:

#ince the indicating beha$ior of a detec-tor tube depends not only on the stro=e$olume but also on the suction charac-teristic of the pump it must be ensuredthat each detector tube is used only withthe prescribed pump. ump tube andother components are designed manufac-tured and calibrated together to form agas detector tube unit. Eser interchangeof pumps and tubes or componentssupplied by different manufacturers may

pro$ide erroneous and in$alid measure-ments of toxic en$ironments.)ccordingly such interchange is notrecommended.

Based on this information a 1ualified professional needs to e$aluate all rele$antinformation and determine that any proposedde$iations from certified systems do in fact

pro$ide ade1uate accuracy and precision before using any ad hoc detector tubemonitoring approaches.




Inter"erences. 3epending on the reaction

principles of the tube and the interferingcompounds that are present the interfer-entsmay cause higher or lower readings comparedto the actual le$el of the target chemical. #ometubes contain reagents that react directly withthe target chemical to produce a color change.%f the air contains substances similar to thetarget substance that also react with thereagents in the detector tube the result will bea higher reading. ;or example many tubesused for chlorine will also react to hydrogensulfide ammonia nitrogen dioxide ethylene

or halides as well with the result being anincrease in the concentration reading due tothese positi$e interf erents. %f any of thesecompounds are present in the air duringsampling the result will not be specific forchlorine. %n some cases the color change in atube is due to a p indicator that responds tothe reaction. 8ith this type of tube any similaracid or basic compound (depending on thetube will react as intereferents gi$ing a higherindication. )n example of this interference ishydrogen chloride in the air causing a higherreading on some hydrogen cyanide detectortubes. 4egati$e interferences manifest them-sel$es as less or no color change when aninterferent is present. #ulfur dioxide forexample when present in an atmosphere beingmeasured for hydrogen sulfide will produce alower reading than the concentration actuallypresent.

) second type of detector tube in$ol$es atwo-step reaction in which the target substanceis oxidi>ed in the pretreatment layer beforereacting with the detecting reagent in theanaly>er layer. %n this case any non-target

compound that also reacts with the oxidi>er(pretreatment reagent may be an interferent ifit causes 0consumption0 of the oxidi>er to adegree that oxidation of the target substance isdiminished thus gi$ing a lower indication. )nexample of such an interferent is aromatichydrocarbons to some trichloroethylenedetector tubes.

#ometimes manufacturers specify that an

interferent will cause a different discolorationof a tube than that specified for thecontaminant of interest. ;or example chlorinecauses a bluish stain in one tube and nitrogendioxide will turn the same tube a pale yellowcolor. Therefore a discoloration significantlydifferent from what is predicted should beconsidered suspicious.

The best pre$ention for erroneous resultsdue to interferences is for the sampling

practitioner to e$aluate this potential prior tosampling using the information pro$ided by

the tube manufacturer.

'emperature Corrections. Chemical reactionsoccurring in detector tubes are temperature-dependent. 8ith some detector tubes reactionrates and physical adsorption of reagents aregreatly influenced by tube temperatures. "ostmanufacturers specify the normal operatingrange for their detector tubes as well as a rangeof temperatures o$er which their tubes willwor=. %f the tube is used at an ambienttemperature that is outside of its normaloperating range the reading must be ad'usted

using factors stated in their instructions. Thetube should not be used at temperatures outsidethe specified allowable temperature range.Generally chemical reaction rates are

proportional to the temperature and $aryingreaction rates can distort the reading. ;orexample when the temperature is significantlylower than +*KC the reaction will slow downand some 1uantity of the sample may not reactin the normal reaction >one but instead will

partially react further down the tube. )s aresult a longer layer of pale color change is

produced gi$ing a higher indication. 8hen thetemperature is significantly higher than +*KCthe rate of reaction will be higher than normaland the most or all of the sample may react in ashorter distance than the normal reaction >onefor +*KC. )s a result a shorter layer of distinctcolor change would be produced gi$ing a








DETECTORTU3ES 720

T)BD< /6.5. Typical Temperature Correction ;actors for #ol$ent 3etector Tube

True Concentration (ppm

Tube &eading (ppm *KC(6+K;

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#11



DETECTORTU3ES

75.

Figure 1".). #chematic of simultaneous direct-reading indicator tubesystem. (&eprinted with permission from Am. nd. /yg. Assoc. . ,,:J//IF6.

%naccessible locations such as utility $aultscan be sampled by using a flexible tubeattached to the pump and putting the detectortube at the other end. The sample should bedrawn directly into the detector tube meaningthat the detector tube should be lowered intothe hole attached to the end of the tubing and

not with the tubing in front of the detectortube. The 0tube in front0 configuration a$oidsthe chance of contaminants adsorbing onto thetubing wall which will result in a low reading.

Dete'tr T!$e P!"& Mai(te(a('e a(Perfr"a('e Che'>s

"aintenance is important for detector tubepumps. ;or example flow orifices may plugfrom glass fragments from the tube openingsand elastic components such as gas=ets may

lose their elasticity from

decomposition products of the detectionreaction or unreacted contaminants passingthrough the tube. umps should be accurate to5 of their stated $olume according to thecurrent performance standards (see Table/6.,., There are two types of performancechec=s that should be conducted on grab

sampling pumps to assure accuracy inmeasurements: lea=age tests and flow ratecalibrations. The E.#. A#) Technical

Manual re1uires that each pump used by theircompliance officers be lea=-tested before useas well as calibrated for proper $olume at least1uarterly or after /** tubes using proceduresdescribed in the ManualH

!eaage 'est. A lea=age test should be performed on each pump in order to minimi>eerroneous readings (due to air lea=s around the

seals when it is first purchased




after an extended period of non-use and

periodically during use in accordance with themanufacturers instructions. %f a pump hasmultiple settings the procedure should berepeated for each setting.

&rocedure. #teps /-, refer to a piston pumpwhile step 5 describes the test for a bellowspump.

5F. %f the pump has multiple orifices turnthe rotating head through se$eralre$olutions finally stopping at the highest

fiowrate position.5I. %nsert an unopened detector tube into

the tube holder. Dine up the guide mar=s(usually dots on the pump shaft andhousing pull bac= the handle all the wayand loc= the piston in the maximum$olume position.

J*. 8ait + minutes and release the pumphandle slowly in order to pre$ent damageas it springs bac=. 8hen the handle isreleased the piston should returncompletely to the *-mD mar=. %f it does

not the pump is not lea=-tight and theamount of lea=age is indicated by the$olume reading as the handle comes torest. %f there is greater than 5mD oflea=age in a /**-mD sample $olumewithin + minutes or whate$er time isre1uired for the normal pump samplingstro=e there is excessi$e lea=age whichshould be repaired to maintain samplingaccuracy.

J/. %f excessi$e lea=age is found it usuallyoccurs either at the pump inlet or between

the piston and cylinder walls. Dea=age inthe cylinder can usually be corrected bycleaning and relubrication. Dea=age at theinlet may result from a poor seal betweenthe detector tube and the rubber inlet tipor between the flange of the rubber inlettip and the pump body.

5. ;or a bellows pump insert an unopened

tube and compress the bellowscompletely. Det it sit for 6* minutes andchec= for obser$able expansion. %f there isnone the pump passes.

Volume and Fiowrate Caliration.Calibrate detector tube pumps for proper$olume measurement 1uarterly. Ane of thereasons the pumps lose their $olume capacityis due to the buildup of particles releasedduring the tubes reactions. These fine particlesare pulled into the interior of the pumps and

gradually build up.The fiowrate (mD!min determines the

reaction rate for many chemical reactions thatoccur in detector tubes so refer to themanufacturers literature for fiowrate criteriaand recommendations for fiowrate tests. #ome

pumps ha$e filters in which case the filtershould be chec=ed for buildup which willreduce fiowrate.

ProcedreJ+. Test the detector tube pump for lea=age

following the procedures pre$iouslydescribed.

J6. Connect the inlet of a detector tube pump to the top of a +**-mD bubble burette using Tygon tubing. ;or pro-cedures on the use of bubble burettes seeChapter 5. ;or pumps with limitingorifices to control fiowrate use a suitableadapter such as a short piece of glasstubing in place of a detector tube (i.e. donot put a detector tube in line for these

pumps. ;or pumps that rely on the

resistance of a detector tube to go$ernairflow rate insert a fresh opened tube inline during measurements.

;or a piston pump continue with steps 6-Jand I? for a bellows pump go to step .








DETECTORTU3ES

75

J,. %f the pump has flow control orificesselect the orifice to be tested.

J5. &e$iew the manufacturers literaturefor the pump being used to determine thenumber of minutes to wait after pullingthe pump handle for the full $olume ofthe pump to be drawn.

JJ. 3ip the bubble burette into bubblesolution and pull the pump handle

slightly to mo$e the bubble front into thecalibrated section of the burette. 4ote theinitial position of the soap bubble. ushthe pump handle bac= in then pull the

pump handle all the way out for a full pump stro=e and time the bubble frontfrom the start until it comes to rest. 4otethe final position (reading of the soap

bubble. The difference between the initialand final points is the sample $olume.The $olume di$ided by the time is theflowrate.

J. Ese the same procedure to test eachorifice for pumps with multiple flowcontrolling orifices.

;or a bellows-type pump follow steps through I.

JF. #1uee>e the pump ma=ing sure the bellows are completely and e$enlycompressed. )llow the pump to open onits own measuring the $olume asdescribed in step 5. &epeat two moretimes and a$erage the three

measurements.JI. Compare the results with the manu-

facturers specification for allowable$ariation in total $olume and the timere1uired to draw the total $olume.

*. &epair the pump if the $olume error isgreater than 5 and repeat the $olumecalibration test.

ield Measurements ith etector 'ubes. Thefirst step is to identify the target chemical(s their approximate

concentration(s any other compounds(potential interferents that are li=ely to be

present during sampling and rele$ant en$i-ronmental conditions such as ambienttemperature and relati$e humidity. 8ith thisinformation the proper tube can be selected.The tube should also be selected for theconcentration range of interest relati$e to theallowable exposure limit? usually this is the)CG% TD@7 or A#) permissible exposure

limit (<D. ;rom the tube instruction sheetnote the number of stro=es and theapproximate time for the sample to becollected. ;or example in order to reach asensiti$ity of / ppm at least one tube for

ben>ene re1uires fi$e stro=es each + minutesin length? thus a single measurement re1uires/* minutes.

%n many cases the sensiti$ity of a readingcan be impro$ed by ta=ing two to fouradditional stro=es and multiplying the finalresult by the ratio of the specified number of

stro=es to the actual number of pump stro=es.;or example if one pump stro=e results in areading below the first concentration mar= of/* ppm two more stro=es can be collected. %fthe reading is now +* ppm that $alue can bedi$ided by 6 to yield a measurement result of ppm which is more specific than reporting a:/*ppm0 reading.

%t is important to =eep the tube inlet in the proper location during the sampling phase. %ffatigue or aw=ward position ma=es holdingthe proper position difficult consider using aTygon tube between the tube and pump. Thetube must remain positioned during the entiresampling period in order to ma=e sure all theair comes from the proper point or source.

Procedre for #ello+s Pmps/. Brea= off the ends of a fresh detector

tube by inserting each end in the tube brea=er hole usually located in the pumphead or by using a separate brea=-offde$ice. 3ispose of the bro=en glass in asafe place. 8ith a




two-tube system connect the ends of the

two tubes using the rubber tubing suppliedafter brea=ing the tube tips. %nsert the tubesecurely into the pump inlet ta=ing carethat the arrow on the tube points towardthe pump.

/. #1uee>e the bellows pump andrelease then wait for the chain straddlingthe bellows to become taut or for the endof the flow indicator to change color.Bellows-type pumps must be compressedcompletely flat to get an accurate sample.Both hands may be needed since e1ual

pressure must be applied to both ends ofthe pump if the entire bellows does notfully compress when only one hand isused. &epeat the compression process asoften as specified in the tubes operatinginstructions. %f using the stro=e counterma=e sure that it registers each stro=e togi$e an accurate count.

+. 8hen drawing air into a tube obser$ethe tube to note any color change or stainde$elopment. ;or example if using ahydrogen sulfide tube with a sensiti$ity

range of *.5 ppm to /.5 ppm based on /*stro=es the tube will fully color with afewer number of stro=es if the concentra-tion is higher than /.5 ppm. 3o not stopuntil the full number of stro=es has been

pulled unless the tube saturates asdescribed abo$e. %f this happens put in anew tube and pull one-half the specifiednumber of stro=es (in this example 5stro=es and multiply the reading by afactor of two.

6. &ead the tubes immediately after

sampling since some changes in thecoloration will occur with time possiblyincluding a complete fading of the stain.8here there is a gradation of color changethe end point should be ta=en as that pointwhere the slight

discoloration can 'ust barely be discerned

from the original color. %f the end pointoccurs at an angle estimate theconcentration for each side of the tube anda$erage them.

Procedre for Piston Pmps,. "a=e sure the pump handle is all the

way in. )lign the index mar=s on thehandle and bac= plate of the pump. Brea=off the ends of a fresh detector tube?dispose of the bro=en glass in a safe place.8ith a two-tube system connect the endsof the two tubes using the rubber tubingsupplied after brea=ing the tube tips. %nsertthe tube securely into the pump inlet ta=ingcare that the arrow on the tube pointstoward the pump.

5. 8ith a multiple orifice pump select the proper orifice by sliding the loc=ing buttonon the rotating head forward and turningthe head to the designated index number onthe flow control plate. 8hen the center lineof the loc=ing button is ad'acent to theindex mar= release the button. The spring-

loaded button will then loc= the rotatinghead in this position.

J. ull the handle straight bac= (withoutturning to the sample $olume re1uired (fullor partial pump stro=e. The piston willautomatically loc= in this position. Ansome models the handle can be loc=ed oneither +5- 5*- or /**-mD (full stro=e.)dditionally some pumps feature a 0one-hand0 $al$e (;igure /6./* that allows thesampling to be initiated with only one handafter the piston has been pulled bac=. The

time re1uired for the pump to draw its full$olume is important and is specified in thetubes literature? it is necessary to allow thisamount of time in order to collect a fullsample. %f the handle is released beforesufficient time has








LONG?TERM COLORIMETRICTU3ES AND 3ADGES

758

Figure 1".1*. 0Ane-hand0 $al$e permitspiston pump sampling with only one handafter the piston is pulled bac=. (Courtesy of4extte1 DDC.

passed the $olume will be smaller than isre1uired with the result being a lowerreading than the concentration that is

actually present. ,. ;or subse1uent stro=esif needed unloc= the pump handle byma=ing a one-1uarter turn and return it tothe starting position. &otate the handle torealign the index mar=s for the next stro=eand pull the handle again. The detector tubeshould remain in place until all the stro=esha$e been made.

Ma@i"i<i(# the A''!ra'% f Dete'tr T!$eMeas!re"e(ts

;ollow these guidelines to maximi>e theaccuracy of detector tube readingsJ:

• 3etector tubes are calibrated at +*KC(JFK; and 5* relati$e humidity. ;ormeasurements at significantly differentconditions use the correction factorssupplied by the manufacturer.

• The shorter the stain length the harder itis for a tube to meet the accuracyspecification (e.g. +5 of a /-mm-longstain is a much smaller

window than +5 of a /*-mm stain. %fse$eral range tubes are a$ailable choosethe tube that will pro$ide a stain length inthe upper two-thirds of the tubes range.

<nsure that the concentration inter$almar=ings on the calibration scale areappropriate for the concentration andsetting being e$aluated. ;or example asulfur dioxide tube with a /- to 5*-ppmrange would not be the best choice formeasuring occupational exposures sincethe permissible exposure limit (<D is+ppm while the tube with a 5*-ppm rangewould probably be mar=ed at 5-ppminter$als. &egular lea= chec=s of the pumpwill help to achie$e optimum accuracy byensuring that the proper air $olume is

passing through the tube. ;resh detectortubes will generally be more accurate thantubes beyond their expiration date. 4e$eruse detector tubes that are past the postedexpiration date.

&efrigerated storage will prolong thefreshness of the tubes and impro$eaccuracy. The recommended storagetemperature is 5-/*KC (,/-5*K;. 3etectortubes should not be stored fro>en.

;or optimum accuracy allow the tubes towarm up to ambient temperature prior touse.

LONG?TERM COLORIMETRIC TU3ES AND 3ADGES

This category of colorimetric de$ices includeslong-term detector tubes direct-reading

badges and 0spot0 plates. Their application issimilar to (a sample collection de!icemethods for gases and $apors and (b

personal-si>e direct-reading instruments withdata-logging capability. )lthough theiraccuracy is not as high as




the accuracy of sorbent tubes analy>ed in the

laboratory there are situations where the use oflong-term detector tubes can be an ad$antage.%n cases where there is a high degree ofemployee concern o$er a potential exposurethese tubes gi$e immediate results that aremore representati$e of employee exposure(integrated than a series of grab samples usingshort-term detector tubes. Dong-term tubes fora $ariety of chemicals can be =ept on hand foroccasional use whereas maintaining anin$entory of direct-reading instruments withfresh sensors for infre1uent measurements may

not be feasible. Dong-term detector tubes canbe $ery useful in situations where a gas or$apor is suspected in that they can be used as ascreening de$ice. They can detect much lowerle$els than other detector tubes because theycan collect samples for a longer period of time.%n a situation where the concern is whatcompound (rather than how much is presentthese tubes can be used for F- to /+- or e$en+,-hour screening samples. %t can be difficultto interpret results when contaminants arepresent at $ery low le$els due to differences incolor changes as compared to the expectedcolor based on a normal sampling time.

%t is especially important to remember thatthese tubes still suffer from the same problemwith interferences as the ones used for grabsamples. Dong-term or long-duration tubes area$ailable for a limited number of compoundsbut for some of these chemicals the tubes fill areal need in some monitoring situations if theonly other a$ailable measurement methods areimpingers or expensi$e real-time instruments.

L(#?Ter" Dete'tr T!$esDong-term detector tubes fall into two designs:(a those that are used with battery-operatedlow-flow personal monitoring pumps for acti$esampling and (b

passi$e de$ices where the contaminants enter

the tube $ia diffusion. These tubes ha$e thesame basic features and characteristics as theshort-term detector tubes described abo$e. Themain difference $isible to the sampling

practitioner is that the calibration scale is notmar=ed in :ppm0 units? instead it is mar=ed inunits of microliters (uD or ppm-hours, and asimple calculation is needed to determine theexposure le$el for comparison to standardsexpressed in units of ppm. The sample time formost tubes $aries from / hour to , hours sose$eral tubes may be needed to measure a full

F-hour time-weighted a$erage exposure.

!ong-'erm 0etector 'ubes "or Pump Sampling. Dong-term tubes for use with a pump usually re1uire $ery low flowrates (inthe range of /*-+*mD!min? not all pumps canachie$e these low rates. The setup is essentiallythe same as that used for gas and $aporsampling with sorbent tubes discussed inChapters 5 and J on sample collection de!icemethods. )s with sorbent tubes the tubesshould be =ept in a $ertical position during use.The tubes should also be chec=ed periodicallyto see if any color change is occurring duringthe sampling period in order to a$oid the

potential of exceeding the tubes capacity. Theinformation in the tubes instruction sheet isimportant since it describes the sampling ratethe total $olume the sampling time and theresponse time for the color change to de$elopas well as temperature humidity and pressurecorrection factors and possible interferents.

8hile the specified sampling time andflowrate must be followed for accurate1uantitati$e measurements some flexibility is

possible when the tubes are used for screeningmeasurements when it is suspected that thetarget chemical is present in $ery lowconcentrations. ;or example $ery low le$elsof sulfur dioxide can cause metal to rust andthese extremely low le$els can








LONG?TERM COLORIMETRICTU3ES AND 3ADGES

750

be detected by sampling with a long-term tubefor a +,-hour period.

Procedre. rior to use test each batch of tubes

with a =nown concentration of the aircontaminant that is to be measured. &eferto the manufacturers data for =eyinformation and a list of interferingmaterials. Abser$e the manufacturersexpiration date and discard outdatedtubes.

F. Brea= off the ends of a tube. Calibratea pump at the specified flowrate usuallylAmD!min to +* mD! min with a properlength of tubing and a long-term tube inline using a bubble burette or electroniccalibrator.

I. )fter calibration replace the tube witha fresh one if there was any possibility ofcontaminants being present or soap filmor water $apor entering the tube duringcalibration. ut the pump on a wor=er orin the area to be sampled. Turn on the

pump and record the time or the stro=enumber if using a stro=e $olume pump.

F*. )t the end of the sampling period turnoff the pump and record the time andalso record the stro=e reading ifappropriate. %f the instructions for thetube re1uire that fresh air be pulledthrough the tube to fully de$elop thecolor change ta=e the tube to an areawhere clean air is present and pull the

re1uired amount of air through it. %f onlya small amount is re1uired such as5**mD then a suction pump such as a

bellows pump can be used? otherwise the battery-operated pump is used.

F/. &ead the tube immediately after thelast amount of air is pulled through it.&ead the length of stain in a well-lightedarea. &ead the longest length

Figure 1".11. Colorimetric diffusion tubes forlong-term measurements. (Courtesy of

4extte1 DDC.

of stain if the stain de$elopment is notsharp or is une$en around the tube inorder to gi$e a conser$ati$e estimate of

exposure. "any tubes will retain theirstain for a period of time if the ends arecapped.

!a""i#e $ete%tor or $o"imeter &ue".assi$e detector or dosimeter tubes (;igure/6.// are a$ailable for a $ariety of chemicals.They operate either based on the length-of-stain or the color intensity that de$elopsfollowing exposure in the atmosphere to betested. Their primary ad$antage o$er the acti$e(pump detector tube method is their ease of

use in that they are simply opened and hung in place for a period of time. They are designedto be exposed and read after a certain numberof hours up to a stated maximum. The basicconcept is that increasing exposure timesresults in longer stain lengths. The stain lengthis thus related to the product of exposure timeand ambient concentration. These de$icesconsist of a glass or plastic tube containing aninert granular material or a strip of paper thathas been impregnated with a chemical systemthat reacts with the gas or $apor of interest. )sa result of this reaction the impregnated

chemical changes color. The granular materialor paper strip is held in place within the glasstube by a porous plug of a suitable inertmaterial. 3uring use the dosimeter tube is heldin a holder that protects the dosime-




ter and also helps to minimi>e effects of air

currents on performance. The holder has a clipthat allows it to be fastened to a collar orpoc=et during personal sampling or to someappropriate ob'ect during area sampling.

The dose is deri$ed from length-of-staindosimeters by reading the length of stain fromthe calibration cur$e pro$ided with the tubes orprinted on the tube. The dose from colorintensity units is obtained by comparing thecolor intensities pro$ided by the manufacturerwith the color that de$elops on the dosimeter.8hen the reading is in units of ppm-hours, this

$alue is di$ided by the number of hours in thesampling period to obtain a time-weighteda$erage (T8) exposure result.

#ome dosimeters are designed to be usedo$er se$eral daysHfor example units placedin homes to measure formaldehyde. Thesede$ices often ha$e a calibration for / daysexposure and for days exposure. Thesedosimeters are usually intended for screeningmeasurements to determine what type if anyof follow-up measurements should be ta=en.&esults are not considered to be precise.

The sampling rate of passi$e colorimet-ricdosimeter tubes is $ery slow on the order of*./ mD!min. Thus the phenomenon that occurswith some passi$e de$ices in low airmo$ement situations where the air layerad'acent to the dosimeter becomes depleted oftarget chemical molecules is not significant forthese de$ices.

;or sampling the dosimeter is either0bro=en0 open or remo$ed from its protecti$ewrapper placed $ertically on the persons lapelor in a gi$en area and the time is recorded. )tthe end of the sample period the time that the

unit is remo$ed is also recorded. The length ofstain or the color intensity is compared withthe standard or measure pro$ided by the manu-facturer which often is a graph ofconcentration cur$es corresponding to stainlength at a gi$en time. By finding the

stain length on the Ix axis0 and drawing a line

to intersect with the point on a cur$e thatcorresponds to the number of hours for whichmonitoring was done the concentration for thesampling period can be determined.

2Spot Plate2 adges. #pot plate badges offeranother option for passi$e colorimet-ricsampling. "ost are designed for $isuale$aluation and ha$e indicator strips or buttonsthat change color when a critical accumulationof the target gas is reached. #ome ha$e thecolors corresponding to $arious concentrations

printed directly on the de$ice or use a coloredicon to warn of ha>ardous le$els while othersmust be compared to a chart to determine theintegrated concentration.

The SAEA1= system (;igure /6./+ is aself-contained unit that warns of the thresholdconcentration of a contaminant because the0exclamation point0 icon becomes $isible. ;orhigher resolution and wider measurementrange a slip-in color comparator is a$ailablefor selected chemicals. The color comparatorcontains a color scale that matches the colorde$eloped on the badge at different ppb-hr or

ppm-hr exposures. Table /6.J shows thechemicals for which the SAEA1 badge andcolor comparator are a$ailable.

#ome spot plate de$ices are designed to beused with a sampling pump to increase theminimum detectable le$el and accuracy. %nother respects these units are similar to the

passi$e de$ices.)n inno$ati$e colorimetric badge by )ssay

Technology relies on an electronic reader tomeasure ethylene oxide exposures. TheChemChipM personal monitor (;igure /6./6

is worn as a badge on poc=et or lapel. )fterwearing the test strips encased in the monitorare remo$ed de$eloped and inserted into acalibrated reflectance colorimeter. Thiselectronic reader pro$ides on-site readout ofchemical exposure in the parts per million(ppm








COLORIMETRIC ELECTRONICINSTRUMENTS

765

Figure 1".1". ChemChipM personal monitoring systemfor determining exposure to ethylene oxide. (Courtesy of)ssay Technology.

COLORIMETRIC ELECTRONICINSTR'MENTS

There are two types of colorimetric electronicinstruments: tape-based monitors and wet chemicalinstruments.

Figure 1".12. Colorimetric badges show animmediate color change upon exposure? some

de$ices also use a color comparator for moreaccurate determination of concentration.(Courtesy of U9" <n$ironmental %nc.

range. The operating range is /*-5** of thepermissible exposure limit with optimalaccuracy in the range of 5*-+** of the <D.%t can reliably measure *./ ppm for an F-hourshift and lppm o$er a /5-minute #T<D periodand it meets A#)s accuracy re1uirementsfor compliance measurements.

T";e/B"sed Mon!torsaper tape-based instruments use chemicallyimpregnated tape to detect toxic gases. Thetape changes color when exposed to the targetgas? the color change is detected by a

photocell analy>ed and translated into aconcentration $alue (;igure /6./,.I Thesede$ices ha$e the ad$antage of pro$iding

physical e$idence of the gas concentrationfrom a lea= or release and typically are less

prone to inferences when compared toelectrochemical and solid-state sensors. )

disad$antage



766 COLORIMETRIC S;STEMS FORGAS AND VAPOR SAMPLING

TABLE 1".$. Target

C'emicals for

SAFEA3; System

Colorimetric Passi0e

Ba+ges

"inimum "aximum "inimu

3etectable #am lin #am linDe$el Time Time

Chemical Threshold De$el (F ours (ours ("inute

)mmonia ,.*ppm-hr *.5*ppm ,F /5

)niline0 *.+ m-hr *.*+5 m ,F 5)rsine /F b-hr +.+5 b /+ /5Carbon dioxide0 F*** m-hr /*** m /* /5Carbon monoxide m-hr l m /* /5Chlorine0 *./F m-hr *.*+6 m ,F /5Chlorine!Chlorine Cl+: *./F m-hr *.*+6 m /* /53ioxide C/*+: *.+ m-hr *.*+5 m3imeth l amine 5 m-hr *.J m ,F 5/ /-3imeth l ;ront: 6* b-hr 6.5 b ,F 5h dra>ine Bac=: lA b-hr /.+5 b

;ormaldeh de *., m-hr *.*5 m /* /5 dra>ine0 F.* b-hr /.* b ,F 5ydrogen

0

+.* ppm +.* ppm#T<D

*.+5 /5

ydrogen0

+.F ppm +.F ppm#T<D *.+5 /5

dro en sulflde + m-hr *.+5 m ,F /5"ercury ;ront: *./

mg!m6-hr*.*/6mg!m6

,F /5

"eth l *.*+5 m-hr *.**F m ,F /* 4itro en dioxide l m-hr *./+5 m /* /5A>one *.*5 m-hr *.**J m ,F /5hos ene0 *.*/5 m-hr *.**+ m + /hos hine0 5.* b-hr *.J+5 b /+ /5#ulfur dioxide *.+ m-hr *.*+5 m ,F /5+ ,-Toluene 5.* b-hr *.J+5 b +, /5

diisocyanate

0 %ndicates that a co



lorcomparator is

a$ailablefor thechemical.Source+9 "<n$ironmental(dmen$ironmental.com

isthat

becauseofcostandcom

p

lexitymostfixed

installatio

nsuseacentr alanaly>erwiths

am

plingtu

besr

untor emo

te locations. Thusthere can be aconsiderable time

delay between arelease and whenthe concentrationis sensed by theinstrument. Thesede$ices are alsorelati$ely complexwith mechanicaloptical andelectronic systemsthat need

pre$enti$emaintenance andmay be prone to

plugging orfailure dependingon the ambienten$ironment.)dditionally thetapes usually needsome

moisture in the airin order tofunction? a relati$e

humidity of ,*is a typicalspecification./*

"oresophisticated tape-

based monitorsuse ad$ancedoptics to measurethe light reflectedoff of the tape

before and afterthe tape is exposedto the sample gasstream. %n somecases there aremultiplemeasurement0windows0Hsomeha$e filters toreduce theinstrumentssensiti$ity andthus increase themeasurementrange. #ometimes

two detection principles are

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COLORIMETRIC ELECTRONICINSTRUMENTS

76.

Figure 1".1#. 3iagram of a tape-basedcolorimetric direct reading instrument.(Courtesy of %nternational #ensorTechnology.

used in order to monitor o$er a wide range ofconcentrations:/*

• ensity mode for low concentrations inwhich the intensity of the stain is

compared to calibration data stored in theinstrument.

• 1ate of change mode which monitorshow fast the stain is de$eloping formeasuring higher concentrations.

Esing both principles is necessary to co$era broad concentration range with a highdegree of accuracy. 8ith the density modethere is a flattening of the concentration-response cur$e as the concentration increasesand the stain approaches its maximum

intensity. Beyond this point a higherconcentration does not produce much increasein stain intensity. The rate of change modecontinually monitors how fast the tape isdar=ening. The higher the concentration thefaster the stain de$elops. The instrument cancalculate the concentration based on how fastthe tape dar=ens.

Tape-based monitors are most commonlyused for isocyanate compounds because of thedifficulty in continuously measuring thesecompounds. Ather compounds for which tape-

based monitors are

offered include phosgene hydra>ineammonia bromine chlorine hydrides (arsinediborane disilane germane hydrogenselenide phosphine silane and stibinehydrogen cyanide hydrogen sulfide nitrogendioxide o>one sulfur dioxide and acid gases(hydrogen bromide hydrogen chloridehydrogen fluoride nitric acid and sulfuricacid. Tape-based monitors are a$ailable assmall passi$e badges personal monitors

stationary monitors and sur$ey instruments.)s with all direct-reading instruments a

potential disad$antage that must be in$es-tigated is the possibility of interference fromother airborne chemicals. #ome inter-ferentswill cause staining of the tape while othercompounds such as sulfur dioxide can bleachthe tape thus causing a lower response. %naddition to e$aluating the possibility ofinterfering compounds during methodselection it is good practice to routinelyinspect the tape following monitoring. %n some

cases it may be readily apparent that aninterferent was present because the color ofthe stain will be different than expected. ;orexample whereas T3% commonly stains a tapered-purple nitrogen dioxide and chlorine willstain the same tape dar= brown.

+utoStep Plus4 Portable Paper 'ape 'oxicGas Monitor. The #cott!Bacharach )utosteplusM is a paper-based colorimetric portablesur$ey instrument for the measurement ofchlorine formaldehyde hydra>ine hydrideshydrogen chloride isocyanate compoundsmono methyl-hydra>ine phosgene and T3%(;igure /6./5. %nstrument operation is basedon the use of $ariable duration discrete sam-

pling periods. )t the start of a period the)uto#tep lus ad$ances to a new piece of tapeand chec=s the stray light and tape bac=groundcolor. %f these are within acceptable limits thereference light le$el is measured and storedand the sampling pump is started pulling airthrough the




Figure 1".1. )utostep lusM tape-based

instrument has tape cassettes for different toxicgases and $apors. (Courtesy of #cott%nstruments.

tape. 3uring the sample period the instrumentcontinuously measures the light reflected off ofthe tape and compares the reading to a presetthreshold. %f a high concentration ofcontaminant is present the reflected light le$elwill e$entually exceed the threshold. 8hen this

happens the sampling period is ended at ,minutes and the stain intensity is used todetermine the concentration. The accuracy iswhiche$er is greater between either Z/5 ofreading or lppb!A.Alppm (depending on thescale.// Two modes of operation allow the)uto#tep lus to effecti$ely operate as both aportable lea= sourcing instrument and atemporary continuous area monitor:

• The 0demand sampling mode0 pro$ides anindication of toxic gas le$els in as little as/5 seconds and is typically used whendetermining the presence or source oflea=s. The user controls the sampling timeand the initiation of new samples.

• The 0continuous sampling mode0 is usefulin area monitoring applications where afixed monitor is not installed or isuna$ailable. The de$ice can monitorcontinuously for up to J*

hours when using @)C line $oltage or up

to +* hours using the built-in lead acid battery. &elay outputs are also pro$ided foran eternal connection to auxiliary warningde$ices.

Cassette life depends upon operationalconditions and the resolution of the instrument.%n standard resolution models where gasconcentration is low cassette life can be asgreat as I** samples (J* hours. )t the otherextreme when operated in conditions wheregas concentrations are $ery high cassette life

can be reduced to F hours. Cassette shelf lifefor unopened cassettes is four months at +*-6*KC and for opened cassettes it is two wee=s.

The )uto#tep lus also functions as a datalogger when used with an optionalcharger!interface unit with software. 8ith thisfeature all readings are stored in non$olatilememory for future readout and analysis. Thiscapability allows results of sur$eys to beanaly>ed and permanently stored. 3ata pointsare stored in memory at the end of eachindi$idual sample period. The duration of these

periods range from +* seconds to , minutesdepending on gas concentration. 3ata can bedownloaded $ia an &#-+6+ serial port and thesoftware controls data downloading analysisstorage and a wide range of displays and

printout options.The instruments DC3 panel shows con-

centration and user-set alarm le$els. %t hasaudible and $isual alarms and an acousticchamber built into the instruments handle also

pro$ides a tactile warning alarm to the user.The acceptable operating range is 6+-/*,K;temperature and 5-I5 relati$e humidity

(noncondensing. Battery ser$ice life of therechargeable lead acid is /J-+* hours and itcan be operated continuously from line $oltagewith the charging unit or interface. The)uto#tep lus is ED appro$ed as intrinsicallysafe for Class % 3i$ision % operation. %t weighs,.5 pounds.






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orimetric de$ices such as tape samplers need

some moisture in the air in order to function.The sampling practitioner must e$aluatepossible interferents and whether the operatingconditions are suitable when determining ifcolorimetric systems are a good option for theirsampling needs.

RE$ERENCES

F+. Cohen B. #. and C. #. "cCammon2r. eds. Air Sampling nstruments for

E!aluation of Atmospheric Contaminants,Ith ed. Cincinnati A: )CG% +***.

F6. log B. ). and . 2. Luinlan eds. undamentals of ndustrial /ygiene, 5thed. %tasca %D: 4ational #afety Council+**+.

F,. #amer #. & and 4. 8. enry. The useof detector tubes ;ollowing )#T" "ethod;-6I-F5 for "easuring ermeation &esis-tance of Clothing. A/A . 5*(J:+IF-6*+/IFI.

F5. )merican 4ational #tandards %nstitute!%nternational #afety <1uipment )ssociation#tandard /*+-/II* (&eaffirmedlIIF.

American *ational Standard for as etec-

tor Tubes H Short Term Type for Toxic

ases and 2apors in Dor'ing En!ironments. )4#%: 4ew Yor= /IIF.

FJ. Technical 4ote (T4-/,6 )ccuracyComparisons of &)< #ystems Gas3etection Tubes. &)< #ystems #unny$aleC) /III.

F. &oberson &. Tech Corner H Commonuestions 1e!ol!ing Around etector Tube

Accuracy. Clearwater ;D: #ensidyne +**6.FF. Uing ". @. . ". <ller and &. 2.

Costello. ) 1ualitati$e sampling de$ice foruse at ha>ardous waste sites. A/A .,,(F:J/5-J/F /IF6.

FI. Accupational #afety and ealth)dministration. (S/A Technical Manual.8ashington 3.C: E.#. 3epartment ofDabor +**6 (http:!!www.osha-slc.go$!dts!osta!otm!otm[extended[toc.html.

I*. Chou 2. /a>ardous as Monitors, A &ractical uide to Selection, (perationand Applications. 4ew Yor=: "cGraw-ill+***.

I/.Dhat Jou Should Kno About as etection. <xton ): #cott!Bacharach Gas

3etection roducts +**6(http:!!www.scottbacharach.com.

I+.Scott0Lacharach AutoStep &lus= &roduct nformation, <xton ): #cott!Bacharach+**6 (http:!!www.scottbacharach.com.

http://www.osha-slc.gov/dts/osta/otm/


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